{"gene":"UBE2I","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":1998,"finding":"UBC9/UBE2I functions as the E2 SUMO-conjugating enzyme, forming thioester intermediates with SMT3 (yeast) and SUMO-1 (mammalian) analogous to ubiquitin-conjugating enzymes; yeast UBC9 is required for SMT3 conjugation in vivo.","method":"In vitro thioester formation assay, in vivo complementation in yeast ubc9 mutant","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro biochemical reconstitution of thioester intermediates plus in vivo genetic complementation, replicated across multiple labs","pmids":["9435231"],"is_preprint":false},{"year":2001,"finding":"SAE1/SAE2 (E1) and Ubc9 (E2) catalyze formation of polymeric SUMO-2 and SUMO-3 chains on protein substrates in vitro; SUMO-2 chains are also detected in vivo. SUMO-1 lacks the consensus ψKXE site and cannot form such chains.","method":"In vitro reconstitution of SUMO chain formation; in vivo detection by immunoblot","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution plus in vivo validation, foundational mechanistic paper","pmids":["11451954"],"is_preprint":false},{"year":2003,"finding":"An N-terminal region of Ubc9 (residues including R13, K14, R17, K18) mediates noncovalent interaction with SUMO-1; mutations at this site (R13A/K14A, R17A/K18A) reduce transfer of SUMO-1 from E1 to E2 without abolishing substrate recognition or SUMO transfer from E2 to target.","method":"Site-directed mutagenesis, isothermal titration calorimetry, in vitro SUMO conjugation assay, NMR chemical shift perturbation","journal":"Biochemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — mutagenesis combined with ITC and in vitro reconstitution, multiple orthogonal methods in one study","pmids":["12924945"],"is_preprint":false},{"year":2004,"finding":"NMR chemical shift perturbation identified the beta-sheet surface of Ubc9 as the binding site for the RanBP2/Nup358 E3 SUMO ligase; this interaction is distinct from classical ubiquitin E2–E3 interactions and is required for SUMO-2 (but not SUMO-1) conjugation to Sp100 and PML. RanBP2 contains a SUMO-1-specific binding site, enabling paralog-selective conjugation.","method":"NMR chemical shift perturbation, site-directed mutagenesis, in vitro SUMO conjugation assays","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — NMR structure-function combined with mutagenesis and biochemical assays, multiple orthogonal methods","pmids":["15608651"],"is_preprint":false},{"year":2005,"finding":"Crystal structure of a four-protein complex (Ubc9, Nup358/RanBP2 E3 ligase domain IR1-M, SUMO-1 conjugated to RanGAP1 C-terminal domain) at 3.0 Å reveals that Nup358/RanBP2 acts as an E3 by binding both SUMO and Ubc9 to position the SUMO–E2 thioester for optimal orientation during conjugation.","method":"X-ray crystallography (3.0 Å), biochemical and kinetic assays with additional substrates","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with kinetic validation, rigorous mechanistic study","pmids":["15931224"],"is_preprint":false},{"year":2005,"finding":"Ubc9 directly purifies as an active SUMO E2: it forms E2~SUMO thioester intermediates and catalyzes SUMO conjugation to consensus ψKXE motifs in substrate proteins in vitro using only E1, Ubc9, mature SUMO, and ATP.","method":"In vitro reconstitution, E2 thioester formation assay, single-turnover and multiple-turnover conjugation assays","journal":"Methods in enzymology","confidence":"High","confidence_rationale":"Tier 1 / Strong — detailed in vitro biochemical reconstitution with defined components","pmids":["16275321"],"is_preprint":false},{"year":2006,"finding":"In budding yeast, distinct functional domains of Ubc9 are required for cell viability versus resistance to DNA damage: swapping domains affecting substrate binding, RanBP2 E3 interaction, and E1/SUMO binding had distinct effects; the activities of E3 ligases Siz1 and Siz2 in genotoxic stress responses were distinguished. Crystal structure of yeast Ubc9 at 1.75 Å resolved these domain functions.","method":"X-ray crystallography (1.75 Å), human/yeast chimera construction, yeast genetic complementation, DNA damage sensitivity assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with chimera genetics and functional assays","pmids":["16782883"],"is_preprint":false},{"year":2007,"finding":"Ubc9 forms a noncovalent complex with SUMO-1 through a surface far from the E2 active site; crystal structure at 2.4 Å shows this interface is conserved with ubiquitin pathway E2–Ubl interactions. Biochemically, this noncovalent interface is less important for E1 activation or di-SUMO-2 formation but important for E3 interactions and for poly-SUMO chain formation beyond two SUMO units.","method":"X-ray crystallography (2.4 Å), in vitro SUMO chain formation assays, E1 activation assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure with biochemical dissection of specific pathway steps","pmids":["17466333"],"is_preprint":false},{"year":2007,"finding":"The noncovalent interaction between Ubc9 and SUMO (via the 'backside' binding site far from the active site) promotes formation of short SUMO chains on substrates Sp100 and HDAC4; crystal structure of the noncovalent Ubc9–SUMO1 complex reveals structural analogy to the Mms2–Ubc13 ubiquitin chain-forming mechanism.","method":"X-ray crystallography, in vitro SUMO chain formation assays, MS identification of chain linkages","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with in vitro reconstitution and mass spectrometry","pmids":["17491593"],"is_preprint":false},{"year":2008,"finding":"Auto-sumoylation of Ubc9 at Lys14 regulates target discrimination: sumoylated Ubc9 impairs activity toward RanGAP1 and strongly activates sumoylation of Sp100 via a SUMO-interacting motif (SIM) in Sp100 that creates an additional interface with the SUMO conjugated to the E2. Crystal structure of sumoylated Ubc9 demonstrates the new binding interface.","method":"Crystal structure of sumoylated Ubc9, in vitro SUMO conjugation assays with multiple substrates, SIM mutagenesis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with biochemical functional assays and mutagenesis","pmids":["18691969"],"is_preprint":false},{"year":2011,"finding":"Crystal structure of Ubc9 in complex with Rad60's SUMO-like domain 2 (SLD2) reveals that Ubc9:SLD2 and Ubc9:SUMO noncovalent complexes are structurally analogous. Disrupting Ubc9:SLD2 selectively impairs Nse2 E3 ligase-dependent DNA repair, while disrupting Ubc9:SUMO noncovalent interaction impairs global sumoylation and SUMO chain formation via Pli1 E3 ligase.","method":"X-ray crystallography, site-directed mutagenesis, yeast genetic epistasis, in vivo sumoylation assays","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure combined with mutagenesis and genetic pathway dissection","pmids":["21444718"],"is_preprint":false},{"year":2012,"finding":"CDK1/cyclin B phosphorylates Ubc9 at Ser71 in vitro; phosphorylated Ubc9 shows increased SUMOylation activity and elevated Ubc9–SUMO1 thioester accumulation. CDK2/cyclin E and other cell cycle kinases tested did not show this activity.","method":"In vitro kinase assay, in vitro SUMO conjugation assay, site-directed mutagenesis (S71A)","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution with mutagenesis but single lab, single study","pmids":["22509284"],"is_preprint":false},{"year":2013,"finding":"Acetylation of Ubc9 at Lys65 selectively downregulates sumoylation of substrates with negatively charged amino acid-dependent sumoylation motifs (NDSM), such as CBP and Elk-1, by attenuating Ubc9 binding to NDSM substrates, without affecting substrates with core ψKXE motif alone. SIRT1 deacetylates Ubc9 K65 under hypoxia, linking this modification to the hypoxia response.","method":"In vitro SUMO conjugation assays, mass spectrometry identification of acetylation site, mutagenesis, siRNA knockdown of SIRT1, reporter assays","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and MS, mechanistic link to SIRT1/hypoxia pathway, single lab but multiple orthogonal methods","pmids":["23395904"],"is_preprint":false},{"year":2013,"finding":"In S. cerevisiae, sumoylation of Ubc9 at Lys153 (Ubc9*SUMO) converts it from an active enzyme into a catalytic cofactor: Ubc9*SUMO is severely impaired in classical SUMO conjugation activity but promotes SUMO chain assembly by cooperating with charged Ubc9 (Ubc9~SUMO) through noncovalent backside SUMO binding, positioning donor SUMO for optimal transfer. A sumoylation-deficient mutant shows reduced meiotic SUMO conjugates and abrogated synaptonemal complex formation.","method":"In vitro SUMO conjugation/chain formation assays, site-directed mutagenesis, yeast genetics (meiotic phenotype), biochemical reconstitution","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis, in vivo genetic phenotype, mechanistic dissection of catalytic vs. cofactor roles","pmids":["23644018"],"is_preprint":false},{"year":2015,"finding":"Akt directly phosphorylates Ubc9 at Thr35; this phosphorylation promotes Ubc9 thioester bond formation with SUMO1, increasing global SUMOylation and substrate-specific SUMOylation (e.g., STAT1, CREB). Akt also phosphorylates SUMO1 at Thr76, stabilizing SUMO1 protein.","method":"In vitro kinase assay, thioester formation assay, site-directed mutagenesis (T35A), co-immunoprecipitation, reporter assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro reconstitution with mutagenesis, single lab, pleiotropic claims","pmids":["25867063"],"is_preprint":false},{"year":2017,"finding":"High-affinity SUMO2 variants (SUBINs) engineered to bind the backside binding site of Ubc9 selectively inhibit poly-SUMO chain formation without impairing mono-SUMOylation, demonstrating that these two activities use distinct surfaces of Ubc9. In cells, SUBINs largely prevent heat shock-triggered poly-SUMOylation and abrogate arsenic-induced PML degradation.","method":"Phage display protein engineering, in vitro SUMO chain formation assays, cellular heat shock and arsenic treatment assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with engineered inhibitors, cellular validation, multiple orthogonal methods","pmids":["28784659"],"is_preprint":false},{"year":2024,"finding":"Pin1 isomerizes Ubc9 in a CDK1-phosphorylation-dependent manner (CDK1-mediated phosphorylation of Ubc9 is required), upregulating Ubc9 thioester formation with SUMO1 and driving SUMO1-modified hypersumoylation in glioma stem cells. Pin1 stability is maintained by USP34-mediated deubiquitination, facilitated by Plk1-mediated phosphorylation of Pin1.","method":"Co-immunoprecipitation, in vitro thioester formation assay, site-directed mutagenesis (CDK1 phosphosite), inhibitor studies (sulfopin, RO3306), in vivo tumor model","journal":"Nature communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, biochemical assays, in vivo tumor model, single lab but multiple orthogonal methods","pmids":["38167292"],"is_preprint":false},{"year":1996,"finding":"Human UBE2I (HsUbc9) interacts with Rad51 recombination protein in a yeast two-hybrid assay, and mouse MmUbc9 protein localizes to synaptonemal complexes in spermatocytes, suggesting a regulatory role in meiosis.","method":"Yeast two-hybrid, immunolocalization in mouse spermatocytes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Low","confidence_rationale":"Tier 3 / Weak — yeast two-hybrid interaction with localization, no direct functional mechanistic follow-up","pmids":["8610150"],"is_preprint":false},{"year":1996,"finding":"UBE2I interacts with RAD52, RAD51, p53, and UBL1 (SUMO-1) in yeast two-hybrid assays; these interactions are UBE2I-specific (RAD6/UBC2 does not interact). The RAD52 interaction is mediated by RAD52's self-association region.","method":"Yeast two-hybrid system","journal":"Genomics","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single method (yeast two-hybrid), no biochemical validation","pmids":["8921390"],"is_preprint":false},{"year":1996,"finding":"Human UBC9 (UBE2I) functionally complements a S. cerevisiae ubc9 temperature-sensitive mutant, rescuing cell cycle progression defects, demonstrating structural and functional conservation.","method":"Yeast genetic complementation","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic complementation assay demonstrating functional conservation, replicated across multiple 1996 papers","pmids":["8668529"],"is_preprint":false},{"year":1999,"finding":"Ubc9 interacts with the androgen receptor (AR) hinge region containing the nuclear localization signal and enhances AR-dependent transcription; a C93S catalytic mutant of Ubc9 that cannot form SUMO-1 thioester still stimulates AR-dependent transactivation, indicating a SUMO-conjugation-independent coregulatory function.","method":"Yeast two-hybrid, co-immunoprecipitation in COS-1 cells, transient transfection reporter assays, C93S mutagenesis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with active-site mutant to separate conjugation from coactivation, single lab","pmids":["10383460"],"is_preprint":false},{"year":2001,"finding":"The IR1+2 domain of RanBP2/Nup358 binds Ubc9 with high affinity in vitro and in vivo; when overexpressed in COS-7 cells, IR1+2 sequesters ~90% of nuclear Ubc9 to the cytoplasm, causing mislocalization of SUMO-1, SUMO-2/3, PML nuclear body enlargement, and cytoplasmic mislocalization of Rad51 with failure to form Rad51 DNA-damage foci, implicating nuclear Ubc9 in Rad51-mediated homologous recombination.","method":"GST pulldown, co-immunoprecipitation, GFP-IR1+2 overexpression with immunofluorescence, DNA damage assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assays combined with subcellular localization experiments and functional consequence (loss of Rad51 foci), single lab","pmids":["11709548"],"is_preprint":false},{"year":2001,"finding":"UBC9 interacts with STRA13 in mammalian cells and promotes its ubiquitin-dependent proteasomal degradation; co-expression of STRA13 and UBC9 leads to increased pSTRA13 ubiquitination, and proteasome inhibitor blocks this degradation.","method":"Yeast two-hybrid, co-immunoprecipitation in mammalian cells, proteasome inhibitor treatment, ubiquitination assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP combined with proteasome inhibitor and ubiquitination assay, though unusual for Ubc9 to directly promote ubiquitination; single lab","pmids":["11278694"],"is_preprint":false},{"year":2003,"finding":"siRNA-mediated knockdown of Ubc9 in HeLa cells reduces endogenous Smad4 levels and intranuclear Smad4 accumulation; SUMO-1 overexpression protects Smad4 from ubiquitin-dependent degradation by competing for the same modification site, leading to enhanced TGF-β transcriptional and growth-inhibitory responses.","method":"siRNA knockdown, SUMO-1 overexpression, subcellular fractionation, half-life analysis of Smad4 mutants, reporter assays","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with mechanistic follow-up comparing sumoylation/ubiquitination competition, single lab","pmids":["12813045"],"is_preprint":false},{"year":2004,"finding":"In budding yeast, Ubc9 and Smt3 (SUMO) are required for efficient APC/C-mediated proteolysis: temperature-sensitive ubc9-2 and smt3-331 mutants show delayed degradation of securin Pds1 and cyclin Clb2 during mitosis, and are defective in chromosome segregation, while proteolysis of non-APC/C substrates is unaffected.","method":"Yeast genetics (temperature-sensitive mutants), cyclin/securin degradation assays, cell cycle analysis, chromosome segregation assays","journal":"Molecular microbiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with temporal substrate degradation assays, single lab","pmids":["14982631"],"is_preprint":false},{"year":2006,"finding":"In S. cerevisiae, Ubc9 and Mms21 SUMO ligase act in concert with Sgs1 helicase to resolve X-shaped cruciform structures at damaged replication forks; ubc9 mutants show Rad51-dependent accumulation of cruciform structures during replication of damaged templates. This SUMOylation function is distinct from the Siz1/PCNA/Srs2 pathway.","method":"Yeast genetics (ubc9 mutant), 2D gel electrophoresis to detect cruciform structures, epistasis analysis with siz1, srs2, pcna, sgs1, top3 mutants","journal":"Cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — rigorous epistasis analysis with molecular readout (2D gel), placed Ubc9 in a specific pathway distinct from Siz1/PCNA","pmids":["17081974"],"is_preprint":false},{"year":2006,"finding":"In zebrafish, reduction of Ubc9 activity (dominant-negative expression or antisense knockdown) causes defects in G2/M transition and mitotic progression, resulting in cells with 4n or 8n DNA content and fewer cells in mitosis in cartilage/eye tissues, without equivalently increasing apoptosis.","method":"Dominant-negative expression, antisense morpholino knockdown, FACS analysis, BrdU incorporation, mitotic marker staining in zebrafish embryos","journal":"Molecular biology of the cell","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo loss-of-function in vertebrate model with cell cycle readouts, single lab","pmids":["17035631"],"is_preprint":false},{"year":2007,"finding":"Ubc9 regulates GLUT4 stability and targeting to the insulin-responsive GLUT4 storage compartment (GSC) in 3T3-L1 adipocytes; overexpression inhibits GLUT4 degradation and promotes GSC targeting, increasing insulin-responsive glucose transport. A catalytically inactive mutant Ubc9-C93A produces the same effects, indicating SUMO-conjugation-independent regulation of GLUT4.","method":"Adenoviral overexpression, siRNA knockdown, glucose transport assay, subcellular fractionation, catalytic mutant (C93A)","journal":"Diabetes","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with catalytic mutant to dissect mechanism, single lab","pmids":["17536066"],"is_preprint":false},{"year":2008,"finding":"UBE2I localizes to nuclear speckles (colocalizing with SFRS2/SC35) in mouse oocytes; overexpression of either wild-type or catalytically inactive UBE2I increases BrUTP incorporation (transcription), demonstrating that transcriptional activation by UBE2I in oocytes is independent of its SUMO-conjugating activity.","method":"Immunocytochemistry, microinjection/overexpression of WT and catalytic mutant, BrUTP incorporation assay","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct localization with functional readout, catalytic mutant used, single lab","pmids":["18703419"],"is_preprint":false},{"year":2009,"finding":"Ubc9 interacts with HIV-1 Gag protein and colocalizes at perinuclear puncta; Ubc9 knockdown reduces virion infectivity 8–10-fold, associated with decreased cell-associated Env glycoprotein stability and altered Env incorporation into virions, without affecting Gag assembly or processing. The catalytic mutant Ubc9-C93A suggests SUMO-conjugating activity may not be required for this function.","method":"RNAi knockdown, colocalization imaging, virion infectivity assay, Env stability assay, catalytic mutant expression","journal":"Journal of virology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RNAi with functional readout and mechanistic dissection using catalytic mutant, single lab","pmids":["19640976"],"is_preprint":false},{"year":2013,"finding":"UBC9 specifically binds the leucine zipper motif of spliced XBP1 (pXBP1(S)) and increases its protein stability; UBC9 knockdown reduces pXBP1(S) levels and ER stress-induced transcription. A SUMO-conjugating-inactive UBC9 mutant equally stabilizes pXBP1(S), indicating SUMOylation-independent stabilization.","method":"Co-immunoprecipitation, siRNA knockdown, reporter assay, catalytic mutant (SUMO-inactive UBC9)","journal":"Cell structure and function","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding with catalytic mutant dissecting SUMOylation independence, single lab","pmids":["23470653"],"is_preprint":false},{"year":2014,"finding":"Synaptic diffusion of Ubc9 in hippocampal neurons is regulated by mGlu5R-dependent signaling: activation of mGlu5R increases Ubc9 synaptic residency time via a Gαq/PLC/Ca2+/PKC cascade, promoting transient PKC phosphorylation-dependent synaptic trapping of Ubc9 and consequent modulation of synaptic sumoylation.","method":"Restricted photobleaching/photoconversion (FRAP/photoconversion) of individual hippocampal spines, pharmacological receptor activation, PKC inhibitor studies","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 2 / Moderate — live imaging with FRAP/photoconversion with pharmacological pathway dissection, novel mechanism, single lab but rigorous","pmids":["25311713"],"is_preprint":false},{"year":2016,"finding":"UBC9 overexpression in cardiomyocytes increases SUMOylation and upregulates autophagic flux; in a proteotoxic model (CryAB-R120G), UBC9 overexpression reduces aggregate formation, decreases fibrosis and hypertrophy, and improves cardiac function and survival, demonstrating that UBC9-mediated SUMOylation promotes cardiac autophagy and protein quality control.","method":"Adenoviral overexpression and siRNA knockdown in neonatal rat cardiomyocytes, transgenic mouse model, autophagic flux assays, cardiac function measurements","journal":"Circulation research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function in vitro and in vivo, mechanistic link to autophagy pathway, single lab","pmids":["27142163"],"is_preprint":false},{"year":2019,"finding":"DNA damage induces nuclear accumulation of UBC9, which SUMOylates lamin A/C; this SUMOylation is required for the interaction between autophagy protein LC3 and lamin A/C, which is required for nucleophagy (degradation of nuclear lamin A/C and leaked nuclear DNA). UBC9 knockdown prevents lamin A/C SUMOylation and attenuates LC3–lamin A/C interaction and nucleophagy.","method":"siRNA knockdown of UBC9, co-immunoprecipitation, immunofluorescence, subcellular fractionation","journal":"Journal of experimental & clinical cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with co-IP and colocalization showing mechanistic pathway, single lab","pmids":["30744690"],"is_preprint":false},{"year":2019,"finding":"UBC9 SUMOylates STAT4 at Lys350 in macrophages; mutation K350R enhances STAT4 nuclear translocation and stability, facilitating proinflammatory macrophage activation. Macrophage-specific Ubc9 deficiency augments CD8+ T cell-mediated antitumor response in prostate cancer.","method":"Biochemical/molecular analysis of SUMO modification site (site-directed mutagenesis K350R), co-immunoprecipitation, macrophage-specific knockout mouse model, tumor growth assays","journal":"The Journal of clinical investigation","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — mutagenesis of SUMO acceptor site with in vivo KO model, single lab","pmids":["36626227"],"is_preprint":false},{"year":2019,"finding":"Ubc9-mediated SUMOylation of IRF4 enhances its nuclear localization and stability, thereby transcribing IL-4 and arginase 1 to promote macrophage M2 polarization; macrophage-specific Ubc9 knockout impairs M2 polarization and exacerbates streptozotocin-induced diabetes.","method":"Macrophage-specific knockout mouse (LyzM-Cre-Ubc9fl/fl), co-immunoprecipitation, subcellular fractionation, gene expression analysis","journal":"Cell death & disease","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell type-specific knockout with biochemical identification of SUMO substrate and functional readout, single lab","pmids":["31767832"],"is_preprint":false},{"year":2019,"finding":"Ubc9/SUMO-conjugase overexpression induces SUMO1-dependent DAT SUMOylation, reduces DAT ubiquitination and lysosomal degradation, enhances DAT plasma membrane steady-state level, and increases dopamine uptake capacity; Ubc9 knockdown has the opposite effects.","method":"Confocal microscopy, FRET, Western blot, RNAi knockdown, dopamine uptake assay","journal":"Frontiers in cellular neuroscience","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — gain- and loss-of-function with functional readout, multiple imaging methods, single lab","pmids":["30828290"],"is_preprint":false},{"year":2019,"finding":"UBC9 interacts with Nedd4-2 E3 ubiquitin ligase (by co-immunoprecipitation) and promotes ubiquitination and proteasomal degradation of Nav1.5 (cardiac sodium channel); UBC9 overexpression decreases Nav1.5 expression and reduces sodium current densities, while UBC9 knockdown has the opposite effect. The C93S catalytic mutant equally regulates Nav1.5, indicating a SUMO-conjugating-independent mechanism.","method":"Co-immunoprecipitation, overexpression/knockdown in HEK293 and cardiomyocytes, patch clamp electrophysiology, proteasome inhibitor (MG132), catalytic mutant (C93S)","journal":"Journal of molecular and cellular cardiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with functional electrophysiology and catalytic mutant dissection, single lab","pmids":["30772377"],"is_preprint":false},{"year":2000,"finding":"Ubc9 interacts with bovine papillomavirus E1 replication protein both in vitro and in vivo; Ubc9 catalyzes covalent SUMO-1 conjugation to E1. An E1 mutant unable to bind Ubc9 shows impaired intranuclear distribution but normal stability, suggesting sumoylation is important for E1 nuclear subdomain localization.","method":"Yeast two-hybrid, in vitro binding, in vivo co-immunoprecipitation, in vitro SUMO-1 conjugation assay, mutational mapping","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro binding and SUMO conjugation assay with functional mutant analysis, single lab","pmids":["10871618"],"is_preprint":false},{"year":2002,"finding":"Loss of Ubc9 in chicken DT40 cells (conditional knockout) causes cell death with increased multinucleated cells (defect in cytokinesis) and apoptosis, rather than the G2/M block seen in yeast ubc9 mutants, demonstrating distinct essential roles of SUMO conjugation in higher eukaryotes.","method":"Conditional gene knockout (tetracycline-repressible transgene), FACS cell cycle analysis, microscopic analysis of nuclear morphology","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO with defined cellular phenotype, single lab","pmids":["12413887"],"is_preprint":false},{"year":2010,"finding":"Inducible knockout of Ubc9 in adult mouse intestinal epithelium causes rapid depletion of intestinal stem cells, loss of the proliferative compartment, disruption of enterocyte polarity (nucleus positioning and actin organization), and detachment from basal lamina. Keratin 8 was identified as a SUMO substrate in intestinal epithelial cells.","method":"Inducible conditional knockout mouse (4-OHT), histology, immunofluorescence, in vitro SUMO conjugation assay for keratin 8","journal":"Gastroenterology","confidence":"High","confidence_rationale":"Tier 2 / Strong — conditional KO in adult mice with precise phenotypic readouts plus substrate identification, rigorous in vivo study","pmids":["20951138"],"is_preprint":false},{"year":2014,"finding":"Ubc9 knockdown stimulates apoptosis in embryonic stem cells (ESCs) but not MEFs; Ubc9 is required for reprogramming MEFs to iPS cells (knockdown dramatically inhibits reprogramming); Ubc9 knockdown decreases expression of pluripotency markers Nanog, Klf4, Oct4, and Sox2 in ESCs.","method":"siRNA knockdown, apoptosis assays, reprogramming efficiency measurement, qRT-PCR for pluripotency markers","journal":"Stem cells (Dayton, Ohio)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with specific phenotypic readouts in defined cell types, single lab","pmids":["24706591"],"is_preprint":false},{"year":2005,"finding":"p14ARF interacts with Ubc9 and enhances SUMO-1 modification of its binding partners (hdm2, E2F-1, HIF-1α, TBP-1, p120E4F); melanoma-associated p14ARF mutations abrogate this sumoylation-enhancing activity, suggesting p14ARF acts as a SUMO E3-like factor through Ubc9.","method":"Co-immunoprecipitation, in vivo sumoylation assays, mutagenesis of p14ARF cancer-associated mutations","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — co-IP with in vivo sumoylation assays, replicated across multiple substrates, but no in vitro reconstitution","pmids":["15876874"],"is_preprint":false},{"year":2018,"finding":"Ubc9 directly binds CRMP2 with low micromolar affinity (measured by microscale thermophoresis and AlphaLISA); disrupting this interaction with a tat-conjugated CRMP2 SUMOylation motif peptide (t-CSM) decreases CRMP2 SUMOylation, reduces NaV1.7 surface trafficking and sodium currents in sensory neurons, and reverses mechanical and thermal hypersensitivity in a spinal nerve injury model.","method":"Microscale thermophoresis, AlphaLISA binding assay, peptide inhibitor, patch clamp electrophysiology, in vivo neuropathic pain model","journal":"Pain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biophysical binding measurements with functional in vitro and in vivo readouts, single lab","pmids":["29847471"],"is_preprint":false},{"year":2008,"finding":"MEL-18 (polycomb protein) interacts with both HSF2 and UBC9; MEL-18 overexpression decreases HSF2 sumoylation and broad cellular protein sumoylation, while MEL-18 knockdown increases them. MEL-18 inhibits UBC9's ability to transfer SUMO to target proteins, functioning as an anti-E3 inhibitor of UBC9 activity. MEL-18 binding to HSF2 decreases during mitosis, correlating with increased mitotic HSF2 sumoylation.","method":"Co-immunoprecipitation, RNAi knockdown, overexpression, in vitro SUMO transfer assay","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP with in vitro SUMO transfer assay and gain/loss-of-function, single lab","pmids":["18211895"],"is_preprint":false},{"year":2022,"finding":"A chimeric E1 enzyme (containing the Ub fold domain of SUMO E1 and remaining domains of Ub E1) activates and loads native ubiquitin onto Ubc9, enabling Ubc9-mediated site-specific ubiquitylation of target proteins bearing a short peptide tag (LACE system) in vitro and in E. coli.","method":"Protein engineering, directed evolution of chimeric E1, in vitro ubiquitylation assay, E. coli co-expression","journal":"ACS central science","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro biochemical reconstitution with engineered enzyme, demonstrates Ubc9 active site can accommodate Ub via modified E1 loading","pmids":["35237717"],"is_preprint":false},{"year":2019,"finding":"Beta cell-specific knockout of Ubc9 in mice causes loss of beta cell mass, increased reactive oxygen species, and diabetes; SUMOylation of NRF2 by Ubc9 promotes NRF2 nuclear expression and transcriptional activity, thereby preventing ROS accumulation. Conversely, Ubc9 overexpression preserves normal blood glucose but impairs insulin secretion.","method":"Conditional knockout and transgenic mouse models (beta cell-specific), ROS measurement, NRF2 subcellular fractionation, immunoprecipitation for SUMOylation","journal":"Diabetologia","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — conditional KO and transgenic models with defined cellular and molecular phenotypes, single lab","pmids":["29299635"],"is_preprint":false},{"year":2019,"finding":"Loss of oocyte-specific Ubc9 in mice causes female infertility with defects in primordial follicle pool stability, folliculogenesis, ovulation and meiosis, and impairs expression of NOBOX and its target genes, demonstrating that SUMOylation in oocytes regulates both oocyte development and communication with granulosa cells.","method":"Oocyte-specific conditional knockout mouse, histology, transcriptomic profiling of ovaries","journal":"Development (Cambridge, England)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cell type-specific conditional KO with transcriptomic analysis, single lab","pmids":["31704792"],"is_preprint":false},{"year":2006,"finding":"siRNA-mediated Ubc9 knockdown severely compromises C2C12 myoblast terminal differentiation and myotube formation without affecting expression, localization, or activation of MyoD or myogenin, placing SUMO-dependent targets downstream of these regulators as required for myogenesis.","method":"siRNA knockdown, Oil Red O staining, immunofluorescence, Western blotting for myogenic factors","journal":"Experimental cell research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — loss-of-function with epistatic placement (downstream of MyoD/myogenin), single lab","pmids":["16631162"],"is_preprint":false},{"year":2017,"finding":"UBC9 is physiologically targeted for degradation by autophagy in human cells; HPV E6/E7 oncoproteins inhibit autophagosome-lysosome fusion, blocking autophagic degradation of UBC9 and leading to p53-dependent UBC9 accumulation during viral transformation.","method":"Ultrastructural analysis (EM), pharmacological and genetic autophagy inhibition/activation, HPV E6/E7 expression, p53 manipulation","journal":"PLoS pathogens","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal approaches (EM, pharmacology, genetics) identifying autophagy as UBC9 degradation pathway, single lab","pmids":["28253371"],"is_preprint":false},{"year":2015,"finding":"UBC9 interacts with the cytoplasmic domain of calnexin (an ER membrane chaperone) and SUMOylates it; this interaction modulates calnexin's association with PTP1B, forming UBC9-dependent calnexin–PTP1B complexes at the ER membrane, linking SUMOylation to ER protein quality control and insulin/leptin signaling regulation.","method":"Co-immunoprecipitation, GST pulldown, in vitro and in vivo SUMO modification assay, immunofluorescence colocalization","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and in vitro SUMOylation with functional consequence of ternary complex, single lab","pmids":["25586181"],"is_preprint":false},{"year":2005,"finding":"Zebrafish Ubc9 interacts with and SUMOylates DeltaNp63alpha; Ubc9-mediated sumoylation (together with Nedd4-mediated ubiquitination) destabilizes DeltaNp63alpha protein on the dorsal side of the embryo. Mutant DeltaNp63alpha unable to bind Ubc9 is stabilized, leading to more widespread neural repression.","method":"Yeast two-hybrid, in vivo sumoylation assay in HEK293 and zebrafish embryos, mutational analysis, rescue experiments in zebrafish","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo sumoylation assays with mutagenesis and in vivo functional phenotype, single lab","pmids":["15908775"],"is_preprint":false},{"year":2011,"finding":"Ubc9 mediates nuclear localization of BRCA1 and BRCA1a; siRNA knockdown of Ubc9 in MCF-7 cells causes enhanced cytoplasmic localization of BRCA1 and exclusive cytoplasmic retention of BRCA1a/BRCA1b, which is associated with loss of growth suppression and ER-α repression activities of BRCA1.","method":"Live cell imaging (YFP/GFP/RFP-tagged BRCA1), siRNA knockdown, colony formation assay","journal":"Journal of cellular physiology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — live imaging with siRNA knockdown linking localization to function, single lab","pmids":["21344391"],"is_preprint":false},{"year":2022,"finding":"FOSL1 promotes UBC9-dependent SUMOylation of CYLD, inducing K63-linked polyubiquitination of NF-κB intermediaries and NF-κB activation, which drives proneural-to-mesenchymal transition in glioblastoma stem cells.","method":"Co-immunoprecipitation, SUMO modification assay, NF-κB reporter, FOSL1 knockdown/overexpression, in vivo tumor model","journal":"Molecular therapy : the journal of the American Society of Gene Therapy","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP and sumoylation assays with in vivo validation, pathway placed with mechanistic detail, single lab","pmids":["35351656"],"is_preprint":false}],"current_model":"UBE2I (UBC9) is the sole E2 SUMO-conjugating enzyme in mammalian cells: it receives activated SUMO from the SAE1/SAE2 E1 heterodimer via a catalytic Cys93 thioester intermediate, directly recognizes consensus ψKXE sumoylation motifs in substrates, and transfers SUMO-1, -2, or -3 to target lysines either alone or in cooperation with E3 ligases (e.g., RanBP2/Nup358, PIAS family); its noncovalent backside interaction with SUMO promotes poly-SUMO chain formation, while autosumoylation at Lys14 and post-translational modifications of Ubc9 itself (phosphorylation by CDK1 at Ser71, acetylation at Lys65 reversed by SIRT1, prolyl isomerization by Pin1) dynamically regulate its activity and substrate selectivity; beyond its enzymatic role, Ubc9 acts as a SUMO-conjugation-independent coactivator/corepressor for multiple nuclear receptors and transcription factors, and is required for cell viability, cytokinesis, G2/M progression, DNA repair, intestinal stem cell maintenance, cardiomyocyte protein quality control, and numerous other cellular processes."},"narrative":{"mechanistic_narrative":"UBE2I (UBC9) is the E2 SUMO-conjugating enzyme that drives protein sumoylation across eukaryotes, receiving activated SUMO from the SAE1/SAE2 E1 heterodimer via a Cys93 thioester intermediate and transferring SUMO-1, -2, or -3 to consensus ψKXE motifs in substrates using only E1, Ubc9, mature SUMO, and ATP [PMID:9435231, PMID:16275321]. Ubc9 directly recognizes substrate sumoylation motifs and cooperates with E3 ligases—RanBP2/Nup358, which binds both SUMO and the Ubc9 β-sheet surface to orient the SUMO~E2 thioester for paralog-selective conjugation, and the yeast Siz/Pli/Mms21 ligases [PMID:15608651, PMID:15931224, PMID:16782883, PMID:21444718]. A noncovalent \"backside\" interaction between Ubc9 and SUMO, structurally analogous to the Mms2–Ubc13 ubiquitin chain-forming mechanism, is dispensable for mono-SUMOylation but required for poly-SUMO chain assembly; engineered backside-binding inhibitors block heat-shock poly-SUMOylation and arsenic-induced PML degradation without affecting mono-SUMOylation [PMID:17466333, PMID:17491593, PMID:28784659]. Ubc9 activity and substrate selectivity are tuned by modifications of the enzyme itself: autosumoylation at Lys14 redirects target discrimination, Lys65 acetylation (reversed by SIRT1 under hypoxia) selectively dampens conjugation of NDSM substrates, CDK1-dependent Ser71 phosphorylation and subsequent Pin1 isomerization enhance thioester formation, and yeast sumoylation at Lys153 converts Ubc9 into a chain-promoting cofactor [PMID:18691969, PMID:23395904, PMID:23644018, PMID:38167292]. Beyond catalysis, Ubc9 acts as a SUMO-conjugation-independent coregulator and protein-stability factor—stimulating androgen-receptor and oocyte transcription, and stabilizing GLUT4, XBP1(S), and other clients via catalytically inactive (C93S/C93A) mutants that retain function [PMID:10383460, PMID:17536066, PMID:18703419, PMID:23470653]. Functionally, Ubc9 is essential for cell viability, cytokinesis and G2/M progression, replication-fork repair, and chromosome segregation [PMID:14982631, PMID:17081974, PMID:17035631, PMID:12413887], and in vivo it maintains intestinal stem cells, oocyte and beta-cell development, cardiomyocyte protein quality control, and macrophage polarization through sumoylation of substrates including keratin 8, NRF2, lamin A/C, STAT4, and IRF4 [PMID:27142163, PMID:30744690, PMID:36626227, PMID:31767832, PMID:20951138, PMID:29299635, PMID:31704792].","teleology":[{"year":1996,"claim":"Established the first physical and genetic links of human UBE2I to recombination/meiosis machinery and demonstrated functional conservation with yeast Ubc9, framing it as a cell-cycle-relevant factor before its enzymatic identity was known.","evidence":"Yeast two-hybrid against Rad51/Rad52/p53/UBL1, spermatocyte immunolocalization, and yeast ts-mutant complementation","pmids":["8610150","8921390","8668529"],"confidence":"Medium","gaps":["Yeast two-hybrid interactions lacked biochemical validation","Did not define a molecular activity for the protein","Meiotic role inferred from localization only"]},{"year":1998,"claim":"Resolved what UBE2I actually does enzymatically: it is the SUMO E2, forming a thioester with SUMO/SMT3 and being required for SUMO conjugation in vivo, defining the entire pathway's E2 step.","evidence":"In vitro thioester formation assay plus in vivo complementation in a yeast ubc9 mutant","pmids":["9435231"],"confidence":"High","gaps":["Did not resolve substrate-selection rules","E3 ligase requirements not yet defined"]},{"year":2001,"claim":"Showed Ubc9 with E1 can build polymeric SUMO-2/-3 chains and that SUMO-1 cannot self-polymerize, distinguishing mono- from poly-SUMOylation as separable outputs.","evidence":"In vitro reconstitution of SUMO chain formation with in vivo immunoblot detection","pmids":["11451954"],"confidence":"High","gaps":["Surface of Ubc9 mediating chain extension not yet mapped","Physiological triggers of chain formation undefined"]},{"year":2003,"claim":"Mapped distinct Ubc9 surfaces for SUMO transfer steps, separating an N-terminal noncovalent SUMO-binding region required for E1-to-E2 transfer from substrate recognition and E2-to-target transfer.","evidence":"Site-directed mutagenesis, ITC, NMR chemical shift perturbation, and in vitro conjugation","pmids":["12924945"],"confidence":"High","gaps":["E3-binding surface not yet defined","In vivo consequence of these surface mutations untested"]},{"year":2004,"claim":"Defined how an E3 (RanBP2/Nup358) engages Ubc9 via its β-sheet surface to confer paralog-selective conjugation, showing SUMO E2–E3 logic differs from ubiquitin.","evidence":"NMR chemical shift perturbation, mutagenesis, and in vitro conjugation of Sp100/PML","pmids":["15608651"],"confidence":"High","gaps":["Mechanism of thioester positioning not yet structurally resolved","Generality across other E3s unknown"]},{"year":2005,"claim":"Provided the structural mechanism of SUMO E3 catalysis: a Ubc9–RanBP2–SUMO~RanGAP1 complex showed the E3 binds both SUMO and Ubc9 to optimally orient the thioester, and parallel work reconstituted the minimal active E2.","evidence":"X-ray crystallography at 3.0 Å with kinetics; detailed in vitro single/multiple-turnover reconstitution","pmids":["15931224","16275321"],"confidence":"High","gaps":["Catalytic chemistry of lysine attack not fully resolved","How modifications of Ubc9 alter this geometry untested here"]},{"year":2007,"claim":"Identified the noncovalent 'backside' Ubc9–SUMO interface as the determinant of poly-SUMO chain elongation, distinct from mono-SUMOylation and analogous to ubiquitin Mms2–Ubc13 chemistry.","evidence":"Crystal structures of noncovalent Ubc9–SUMO1, chain-formation assays, MS linkage analysis","pmids":["17466333","17491593"],"confidence":"High","gaps":["In vivo importance of backside binding not yet probed","Substrate determinants directing chain vs. mono unclear"]},{"year":2008,"claim":"Showed autosumoylation at Lys14 is a self-encoded switch that retunes Ubc9 substrate discrimination, creating a SIM-dependent interface that favors some substrates over others.","evidence":"Crystal structure of sumoylated Ubc9, conjugation assays with multiple substrates, SIM mutagenesis","pmids":["18691969"],"confidence":"High","gaps":["Cellular regulation of Ubc9 autosumoylation undefined","Breadth of SIM-dependent substrates not catalogued"]},{"year":2011,"claim":"Demonstrated that Ubc9 uses analogous noncovalent surfaces to engage SUMO and a SUMO-like domain (Rad60 SLD2), partitioning its activities between Nse2-dependent DNA repair and Pli1-dependent global sumoylation/chain formation.","evidence":"Crystallography, mutagenesis, and yeast genetic epistasis with in vivo sumoylation assays","pmids":["21444718"],"confidence":"High","gaps":["Mammalian counterpart of SLD2 partitioning unconfirmed","How surfaces are selected in vivo unknown"]},{"year":2013,"claim":"Revealed multiple covalent modifications of Ubc9 (Lys65 acetylation reversed by SIRT1; Lys153 sumoylation in yeast) that switch substrate selectivity and convert Ubc9 between active enzyme and chain-promoting cofactor, linking sumoylation to hypoxia and meiosis.","evidence":"In vitro conjugation/chain assays, MS site mapping, mutagenesis, SIRT1 knockdown, yeast meiotic genetics","pmids":["23395904","23644018"],"confidence":"High","gaps":["Enzymes installing Lys153 sumoylation in vivo not fully defined","Crosstalk among the various Ubc9 modifications unresolved"]},{"year":2016,"claim":"Engineered backside-binding inhibitors (SUBINs) provided a tool that selectively blocks poly-SUMO chains in cells, confirming the two activities are pharmacologically separable and required for stress-induced PML degradation.","evidence":"Phage-display protein engineering, in vitro chain assays, cellular heat-shock and arsenic treatment","pmids":["28784659"],"confidence":"High","gaps":["Endogenous regulators that gate backside binding unknown","Range of chain-dependent processes in cells not mapped"]},{"year":2015,"claim":"Extended kinase control of Ubc9 by showing Akt phosphorylates Thr35 to boost thioester formation and global SUMOylation, integrating sumoylation with growth-factor signaling.","evidence":"In vitro kinase and thioester assays, T35A mutagenesis, co-IP, reporter assays","pmids":["25867063"],"confidence":"Medium","gaps":["Single lab with pleiotropic claims spanning STAT1/CREB and SUMO1 stabilization","In vivo significance of Thr35 phosphorylation untested"]},{"year":2024,"claim":"Connected CDK1 phosphorylation of Ubc9 to Pin1 prolyl isomerization as a sequential activation module driving hypersumoylation in glioma stem cells.","evidence":"Co-IP, in vitro thioester assays, phosphosite mutagenesis, inhibitor studies, in vivo tumor model","pmids":["38167292"],"confidence":"Medium","gaps":["Single lab; generality beyond glioma stem cells unknown","Direct structural effect of isomerization on the active site not resolved"]},{"year":2002,"claim":"Established Ubc9 as essential in vertebrate cells with a cytokinesis defect distinct from the yeast G2/M block, showing SUMO conjugation has organism-specific essential roles.","evidence":"Tetracycline-repressible conditional knockout in DT40 cells with FACS and nuclear morphology analysis","pmids":["12413887"],"confidence":"Medium","gaps":["Critical SUMO substrates for cytokinesis not identified","Single cell-type system"]},{"year":2006,"claim":"Placed Ubc9/SUMO in a defined replication-repair pathway, acting with Mms21 and Sgs1 to resolve damaged-fork cruciforms separately from the Siz1/PCNA/Srs2 route, and in vertebrate G2/M control.","evidence":"Yeast genetics with 2D-gel cruciform readout and epistasis; zebrafish dominant-negative/morpholino with cell-cycle FACS","pmids":["17081974","17035631"],"confidence":"High","gaps":["Direct SUMO substrates at the fork not pinpointed","Mechanistic basis of zebrafish G2/M arrest unresolved"]},{"year":1999,"claim":"Uncovered a SUMO-conjugation-independent coregulatory function: a catalytic-dead Ubc9 still potentiates androgen-receptor transactivation, separating enzymatic from scaffolding roles.","evidence":"Yeast two-hybrid, co-IP, reporter assays with C93S mutant","pmids":["10383460"],"confidence":"Medium","gaps":["Structural basis of conjugation-independent coactivation unknown","Breadth across nuclear receptors not tested here"]},{"year":2007,"claim":"Generalized the conjugation-independent role to membrane-protein trafficking, with catalytically inactive Ubc9 (C93A) regulating GLUT4 stability and storage-compartment targeting.","evidence":"Adenoviral overexpression/siRNA in adipocytes, glucose transport, fractionation, C93A mutant","pmids":["17536066"],"confidence":"Medium","gaps":["Partner proteins mediating GLUT4 effect undefined","Whether SUMO of a third party is required not excluded"]},{"year":2010,"claim":"Demonstrated an essential in vivo tissue-maintenance role: inducible intestinal knockout depletes stem cells and disrupts epithelial polarity, with keratin 8 identified as a SUMO target.","evidence":"Inducible conditional knockout mouse, histology/IF, in vitro keratin-8 sumoylation","pmids":["20951138"],"confidence":"High","gaps":["Causal substrate(s) for stem-cell loss not established","Link between keratin-8 sumoylation and phenotype indirect"]},{"year":2019,"claim":"Defined specific substrate-level mechanisms in vivo across tissues—lamin A/C for nucleophagy, STAT4 and IRF4 for macrophage polarization, NRF2 for beta-cell ROS defense, plus oocyte fertility—anchoring Ubc9's physiology to named substrates.","evidence":"Cell-type-specific knockouts, SUMO-site mutagenesis (e.g., STAT4 K350R), co-IP, fractionation, in vivo disease/tumor models","pmids":["30744690","36626227","31767832","29299635","31704792"],"confidence":"Medium","gaps":["Each substrate axis is single-lab","Whether SUMOylation is sufficient versus necessary not fully isolated for all targets"]},{"year":2018,"claim":"Showed therapeutically tractable substrate engagement: Ubc9 binds CRMP2 at low-micromolar affinity, and peptide disruption reduces NaV1.7 trafficking and reverses neuropathic pain, illustrating substrate-targeted modulation of Ubc9.","evidence":"Microscale thermophoresis, AlphaLISA, peptide inhibitor, patch clamp, in vivo nerve-injury model","pmids":["29847471"],"confidence":"Medium","gaps":["Selectivity of the peptide for the Ubc9–CRMP2 interface incompletely defined","Single lab"]},{"year":2022,"claim":"Demonstrated Ubc9 active-site plasticity by engineering a chimeric E1 that loads native ubiquitin onto Ubc9, enabling tag-directed ubiquitylation, showing the catalytic cleft can accommodate ubiquitin.","evidence":"Directed evolution of chimeric E1, in vitro ubiquitylation, E. coli reconstitution","pmids":["35237717"],"confidence":"High","gaps":["Native cellular relevance of ubiquitin loading unknown","Engineered system only"]},{"year":null,"claim":"How the diverse Ubc9 inputs—covalent modifications, backside/SLD surfaces, E3 partners, and conjugation-independent scaffolding—are integrated to select among hundreds of substrates in a given cell state remains unresolved.","evidence":"No single study in the corpus reconciles the regulatory layers into a predictive substrate-selection model","pmids":[],"confidence":"Medium","gaps":["No unified model linking Ubc9 PTMs to substrate choice in vivo","Conjugation-independent functions lack defined structural mechanism","Relative in vivo contribution of mono- vs poly-SUMOylation per process unmapped"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[0,3,4,5,8,34]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[0,5,13,45]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[0,5]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[20,27,28,30]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[4,7,13]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[21,28,33,52]},{"term_id":"GO:0005654","term_label":"nucleoplasm","supporting_discovery_ids":[28]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[21]}],"pathway":[{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[0,1,5]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[24,26,39]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[25,33]},{"term_id":"R-HSA-9612973","term_label":"Autophagy","supporting_discovery_ids":[32,33,49]},{"term_id":"R-HSA-168256","term_label":"Immune System","supporting_discovery_ids":[34,35]}],"complexes":["SAE1/SAE2–Ubc9 SUMO E1–E2 system","Ubc9–RanBP2/Nup358–SUMO1–RanGAP1 E3 complex"],"partners":["SUMO1","RANBP2","SAE2","RAD51","RAD52","PIAS/SIZ/MMS21 (NSE2)","MEL-18","CRMP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P63279","full_name":"SUMO-conjugating enzyme UBC9","aliases":["RING-type E3 SUMO transferase UBC9","SUMO-protein ligase","Ubiquitin carrier protein 9","Ubiquitin carrier protein I","Ubiquitin-conjugating enzyme E2 I","Ubiquitin-protein ligase I","p18"],"length_aa":158,"mass_kda":18.0,"function":"Accepts the ubiquitin-like proteins SUMO1, SUMO2, SUMO3, SUMO4 and SUMO1P1/SUMO5 from the UBLE1A-UBLE1B E1 complex and catalyzes their covalent attachment to other proteins with the help of an E3 ligase such as RANBP2, CBX4 and ZNF451. Can catalyze the formation of poly-SUMO chains. Necessary for sumoylation of FOXL2 and KAT5. Essential for nuclear architecture and chromosome segregation. Sumoylates p53/TP53 at 'Lys-386'. Mediates sumoylation of ERCC6 which is essential for its transcription-coupled nucleotide excision repair activity (PubMed:26620705). Sumoylates SHMT1 at 'Lys-38' or 'Lys-39' leading to RAN-dependent nuclear import of SHMT1 (PubMed:17446168). Also sumoylates TYMS and DHFR (PubMed:18067453)","subcellular_location":"Nucleus; Cytoplasm; Cytoplasm, perinuclear region","url":"https://www.uniprot.org/uniprotkb/P63279/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/UBE2I","classification":"Common Essential","n_dependent_lines":1204,"n_total_lines":1208,"dependency_fraction":0.9966887417218543},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RANBP2","stoichiometry":10.0},{"gene":"XPO1","stoichiometry":10.0},{"gene":"RAN","stoichiometry":4.0},{"gene":"SAE1","stoichiometry":4.0},{"gene":"CLIP1","stoichiometry":0.2},{"gene":"KPNA4","stoichiometry":0.2},{"gene":"KPNB1","stoichiometry":0.2},{"gene":"NUMA1","stoichiometry":0.2},{"gene":"NUTF2","stoichiometry":0.2},{"gene":"NXT2","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/UBE2I","total_profiled":1310},"omim":[{"mim_id":"616910","title":"IMMUNODEFICIENCY-CENTROMERIC INSTABILITY-FACIAL ANOMALIES SYNDROME 3; ICF3","url":"https://www.omim.org/entry/616910"},{"mim_id":"615875","title":"RWD DOMAIN-CONTAINING PROTEIN 3; RWDD3","url":"https://www.omim.org/entry/615875"},{"mim_id":"615708","title":"ZINC FINGER PROTEIN 451; ZNF451","url":"https://www.omim.org/entry/615708"},{"mim_id":"615211","title":"UBIQUITIN-LIKE PROTEIN CONTAINING PHD AND RING FINGER DOMAINS 2, E3 UBIQUITIN PROTEIN LIGASE; UHRF2","url":"https://www.omim.org/entry/615211"},{"mim_id":"613295","title":"UBIQUITIN-LIKE MODIFIER-ACTIVATING ENZYME 2; UBA2","url":"https://www.omim.org/entry/613295"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UBE2I"},"hgnc":{"alias_symbol":["UBC9"],"prev_symbol":[]},"alphafold":{"accession":"P63279","domains":[{"cath_id":"3.10.110.10","chopping":"1-158","consensus_level":"medium","plddt":97.3472,"start":1,"end":158}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P63279","model_url":"https://alphafold.ebi.ac.uk/files/AF-P63279-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P63279-F1-predicted_aligned_error_v6.png","plddt_mean":97.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBE2I","jax_strain_url":"https://www.jax.org/strain/search?query=UBE2I"},"sequence":{"accession":"P63279","fasta_url":"https://rest.uniprot.org/uniprotkb/P63279.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P63279/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P63279"}},"corpus_meta":[{"pmid":"11451954","id":"PMC_11451954","title":"Polymeric chains of SUMO-2 and SUMO-3 are conjugated to protein substrates by SAE1/SAE2 and Ubc9.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11451954","citation_count":697,"is_preprint":false},{"pmid":"15931224","id":"PMC_15931224","title":"Insights into E3 ligase activity revealed by a SUMO-RanGAP1-Ubc9-Nup358 complex.","date":"2005","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/15931224","citation_count":418,"is_preprint":false},{"pmid":"17081974","id":"PMC_17081974","title":"Ubc9- and mms21-mediated sumoylation counteracts recombinogenic events at damaged replication forks.","date":"2006","source":"Cell","url":"https://pubmed.ncbi.nlm.nih.gov/17081974","citation_count":247,"is_preprint":false},{"pmid":"9435231","id":"PMC_9435231","title":"The ubiquitin-like proteins SMT3 and SUMO-1 are conjugated by the UBC9 E2 enzyme.","date":"1998","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/9435231","citation_count":195,"is_preprint":false},{"pmid":"18691969","id":"PMC_18691969","title":"Ubc9 sumoylation regulates SUMO target discrimination.","date":"2008","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/18691969","citation_count":186,"is_preprint":false},{"pmid":"17491593","id":"PMC_17491593","title":"Noncovalent interaction between Ubc9 and SUMO promotes SUMO chain formation.","date":"2007","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/17491593","citation_count":174,"is_preprint":false},{"pmid":"15735760","id":"PMC_15735760","title":"A role for Ubc9 in tumorigenesis.","date":"2005","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/15735760","citation_count":159,"is_preprint":false},{"pmid":"12813045","id":"PMC_12813045","title":"SUMO-1/Ubc9 promotes nuclear accumulation and metabolic stability of tumor suppressor Smad4.","date":"2003","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12813045","citation_count":155,"is_preprint":false},{"pmid":"10383460","id":"PMC_10383460","title":"Ubc9 interacts with the androgen receptor and activates receptor-dependent transcription.","date":"1999","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10383460","citation_count":153,"is_preprint":false},{"pmid":"8610150","id":"PMC_8610150","title":"Mammalian ubiquitin-conjugating enzyme Ubc9 interacts with Rad51 recombination protein and localizes in synaptonemal complexes.","date":"1996","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/8610150","citation_count":144,"is_preprint":false},{"pmid":"15608651","id":"PMC_15608651","title":"Unique binding interactions among Ubc9, SUMO and RanBP2 reveal a mechanism for SUMO paralog selection.","date":"2004","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15608651","citation_count":128,"is_preprint":false},{"pmid":"8921390","id":"PMC_8921390","title":"Associations of UBE2I with RAD52, UBL1, p53, and RAD51 proteins in a yeast two-hybrid system.","date":"1996","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/8921390","citation_count":127,"is_preprint":false},{"pmid":"17466333","id":"PMC_17466333","title":"Structure and analysis of a complex between SUMO and Ubc9 illustrates features of a conserved E2-Ubl interaction.","date":"2007","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/17466333","citation_count":125,"is_preprint":false},{"pmid":"19223510","id":"PMC_19223510","title":"MicroRNA-mediated regulation of Ubc9 expression in cancer cells.","date":"2009","source":"Clinical cancer research : an official journal of the American Association for Cancer Research","url":"https://pubmed.ncbi.nlm.nih.gov/19223510","citation_count":104,"is_preprint":false},{"pmid":"20023705","id":"PMC_20023705","title":"Ubc9 promotes breast cell invasion and metastasis in a sumoylation-independent manner.","date":"2009","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/20023705","citation_count":97,"is_preprint":false},{"pmid":"12413887","id":"PMC_12413887","title":"Ubc9 is essential for viability of higher eukaryotic cells.","date":"2002","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/12413887","citation_count":97,"is_preprint":false},{"pmid":"11278694","id":"PMC_11278694","title":"Regulation of STRA13 by the von Hippel-Lindau tumor suppressor protein, hypoxia, and the UBC9/ubiquitin proteasome degradation pathway.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11278694","citation_count":93,"is_preprint":false},{"pmid":"12924945","id":"PMC_12924945","title":"Role of an N-terminal site of Ubc9 in SUMO-1, -2, and -3 binding and conjugation.","date":"2003","source":"Biochemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12924945","citation_count":84,"is_preprint":false},{"pmid":"8668529","id":"PMC_8668529","title":"Identification of the structural and functional human homolog of the yeast ubiquitin conjugating enzyme UBC9.","date":"1996","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/8668529","citation_count":82,"is_preprint":false},{"pmid":"20561671","id":"PMC_20561671","title":"Expression analysis of Ubc9, the single small ubiquitin-like modifier (SUMO) E2 conjugating enzyme, in normal and malignant tissues.","date":"2010","source":"Human pathology","url":"https://pubmed.ncbi.nlm.nih.gov/20561671","citation_count":81,"is_preprint":false},{"pmid":"11812797","id":"PMC_11812797","title":"Ubc9 is a novel modulator of the induction properties of glucocorticoid receptors.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11812797","citation_count":78,"is_preprint":false},{"pmid":"16300471","id":"PMC_16300471","title":"Targeting Ubc9 for cancer therapy.","date":"2005","source":"Expert opinion on therapeutic targets","url":"https://pubmed.ncbi.nlm.nih.gov/16300471","citation_count":73,"is_preprint":false},{"pmid":"12072434","id":"PMC_12072434","title":"Transcription factor AP-2 interacts with the SUMO-conjugating enzyme UBC9 and is sumolated in vivo.","date":"2002","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/12072434","citation_count":72,"is_preprint":false},{"pmid":"17105732","id":"PMC_17105732","title":"Coactivation of the N-terminal transactivation of mineralocorticoid receptor by Ubc9.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17105732","citation_count":69,"is_preprint":false},{"pmid":"23644018","id":"PMC_23644018","title":"Ubc9 sumoylation controls SUMO chain formation and meiotic synapsis in Saccharomyces cerevisiae.","date":"2013","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/23644018","citation_count":67,"is_preprint":false},{"pmid":"35351656","id":"PMC_35351656","title":"FOSL1 promotes proneural-to-mesenchymal transition of glioblastoma stem cells via UBC9/CYLD/NF-κB axis.","date":"2022","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/35351656","citation_count":67,"is_preprint":false},{"pmid":"8733011","id":"PMC_8733011","title":"Interaction of the Ubc9 human homologue with c-Jun and with the glucocorticoid receptor.","date":"1996","source":"Steroids","url":"https://pubmed.ncbi.nlm.nih.gov/8733011","citation_count":67,"is_preprint":false},{"pmid":"25867063","id":"PMC_25867063","title":"SUMO modification of Akt regulates global SUMOylation and substrate SUMOylation specificity through Akt phosphorylation of Ubc9 and SUMO1.","date":"2015","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/25867063","citation_count":67,"is_preprint":false},{"pmid":"27142163","id":"PMC_27142163","title":"UBC9-Mediated Sumoylation Favorably Impacts Cardiac Function in Compromised Hearts.","date":"2016","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/27142163","citation_count":65,"is_preprint":false},{"pmid":"15876874","id":"PMC_15876874","title":"p14ARF interacts with the SUMO-conjugating enzyme Ubc9 and promotes the sumoylation of its binding partners.","date":"2005","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/15876874","citation_count":65,"is_preprint":false},{"pmid":"29299635","id":"PMC_29299635","title":"Both conditional ablation and overexpression of E2 SUMO-conjugating enzyme (UBC9) in mouse pancreatic beta cells result in impaired beta cell function.","date":"2018","source":"Diabetologia","url":"https://pubmed.ncbi.nlm.nih.gov/29299635","citation_count":64,"is_preprint":false},{"pmid":"17035631","id":"PMC_17035631","title":"Ubc9 regulates mitosis and cell survival during zebrafish development.","date":"2006","source":"Molecular biology of the cell","url":"https://pubmed.ncbi.nlm.nih.gov/17035631","citation_count":63,"is_preprint":false},{"pmid":"30744690","id":"PMC_30744690","title":"Nuclear accumulation of UBC9 contributes to SUMOylation of lamin A/C and nucleophagy in response to DNA damage.","date":"2019","source":"Journal of experimental & clinical cancer research : CR","url":"https://pubmed.ncbi.nlm.nih.gov/30744690","citation_count":63,"is_preprint":false},{"pmid":"17536066","id":"PMC_17536066","title":"The SUMO conjugating enzyme Ubc9 is a regulator of GLUT4 turnover and targeting to the insulin-responsive storage compartment in 3T3-L1 adipocytes.","date":"2007","source":"Diabetes","url":"https://pubmed.ncbi.nlm.nih.gov/17536066","citation_count":63,"is_preprint":false},{"pmid":"20951138","id":"PMC_20951138","title":"Sumoylation by Ubc9 regulates the stem cell compartment and structure and function of the intestinal epithelium in mice.","date":"2010","source":"Gastroenterology","url":"https://pubmed.ncbi.nlm.nih.gov/20951138","citation_count":59,"is_preprint":false},{"pmid":"21147068","id":"PMC_21147068","title":"Over-accumulation of nuclear IGF-1 receptor in tumor cells requires elevated expression of the receptor and the SUMO-conjugating enzyme Ubc9.","date":"2010","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/21147068","citation_count":59,"is_preprint":false},{"pmid":"18703419","id":"PMC_18703419","title":"UBE2I (UBC9), a SUMO-conjugating enzyme, localizes to nuclear speckles and stimulates transcription in mouse oocytes.","date":"2008","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/18703419","citation_count":57,"is_preprint":false},{"pmid":"25097219","id":"PMC_25097219","title":"Sumo E2 enzyme UBC9 is required for efficient protein quality control in cardiomyocytes.","date":"2014","source":"Circulation research","url":"https://pubmed.ncbi.nlm.nih.gov/25097219","citation_count":56,"is_preprint":false},{"pmid":"14982631","id":"PMC_14982631","title":"Smt3/SUMO and Ubc9 are required for efficient APC/C-mediated proteolysis in budding yeast.","date":"2004","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/14982631","citation_count":56,"is_preprint":false},{"pmid":"28143738","id":"PMC_28143738","title":"Manipulating PML SUMOylation via Silencing UBC9 and RNF4 Regulates Cardiac Fibrosis.","date":"2017","source":"Molecular therapy : the journal of the American Society of Gene Therapy","url":"https://pubmed.ncbi.nlm.nih.gov/28143738","citation_count":56,"is_preprint":false},{"pmid":"15908775","id":"PMC_15908775","title":"Destabilization of DeltaNp63alpha by Nedd4-mediated ubiquitination and Ubc9-mediated sumoylation, and its implications on dorsoventral patterning of the zebrafish embryo.","date":"2005","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/15908775","citation_count":56,"is_preprint":false},{"pmid":"36626227","id":"PMC_36626227","title":"UBC9 deficiency enhances immunostimulatory macrophage activation and subsequent antitumor T cell response in prostate cancer.","date":"2023","source":"The Journal of clinical investigation","url":"https://pubmed.ncbi.nlm.nih.gov/36626227","citation_count":54,"is_preprint":false},{"pmid":"31767832","id":"PMC_31767832","title":"Loss of ubiquitin-conjugating enzyme E2 (Ubc9) in macrophages exacerbates multiple low-dose streptozotocin-induced diabetes by attenuating M2 macrophage polarization.","date":"2019","source":"Cell death & disease","url":"https://pubmed.ncbi.nlm.nih.gov/31767832","citation_count":54,"is_preprint":false},{"pmid":"10871618","id":"PMC_10871618","title":"Bovine papillomavirus E1 protein is sumoylated by the host cell Ubc9 protein.","date":"2000","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/10871618","citation_count":53,"is_preprint":false},{"pmid":"23395904","id":"PMC_23395904","title":"Ubc9 acetylation modulates distinct SUMO target modification and hypoxia response.","date":"2013","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/23395904","citation_count":53,"is_preprint":false},{"pmid":"29847471","id":"PMC_29847471","title":"Inhibition of the Ubc9 E2 SUMO-conjugating enzyme-CRMP2 interaction decreases NaV1.7 currents and reverses experimental neuropathic pain.","date":"2018","source":"Pain","url":"https://pubmed.ncbi.nlm.nih.gov/29847471","citation_count":52,"is_preprint":false},{"pmid":"28253371","id":"PMC_28253371","title":"Autophagy regulates UBC9 levels during viral-mediated tumorigenesis.","date":"2017","source":"PLoS pathogens","url":"https://pubmed.ncbi.nlm.nih.gov/28253371","citation_count":51,"is_preprint":false},{"pmid":"22509284","id":"PMC_22509284","title":"Phosphorylation of Ubc9 by Cdk1 enhances SUMOylation activity.","date":"2012","source":"PloS one","url":"https://pubmed.ncbi.nlm.nih.gov/22509284","citation_count":50,"is_preprint":false},{"pmid":"21444718","id":"PMC_21444718","title":"DNA repair and global sumoylation are regulated by distinct Ubc9 noncovalent complexes.","date":"2011","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/21444718","citation_count":48,"is_preprint":false},{"pmid":"8565643","id":"PMC_8565643","title":"Cloning, expression, and mapping of UBE2I, a novel gene encoding a human homologue of yeast ubiquitin-conjugating enzymes which are critical for regulating the cell cycle.","date":"1996","source":"Cytogenetics and cell genetics","url":"https://pubmed.ncbi.nlm.nih.gov/8565643","citation_count":46,"is_preprint":false},{"pmid":"11709548","id":"PMC_11709548","title":"Perturbation of SUMOlation enzyme Ubc9 by distinct domain within nucleoporin RanBP2/Nup358.","date":"2001","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/11709548","citation_count":46,"is_preprint":false},{"pmid":"21880185","id":"PMC_21880185","title":"Ubc9 expression predicts chemoresistance in breast cancer.","date":"2011","source":"Chinese journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/21880185","citation_count":46,"is_preprint":false},{"pmid":"23187003","id":"PMC_23187003","title":"microRNA-214-mediated UBC9 expression in glioma.","date":"2012","source":"BMB reports","url":"https://pubmed.ncbi.nlm.nih.gov/23187003","citation_count":45,"is_preprint":false},{"pmid":"15611122","id":"PMC_15611122","title":"Ubc9 and Protein Inhibitor of Activated STAT 1 Activate Chicken Ovalbumin Upstream Promoter-Transcription Factor I-mediated Human CYP11B2 Gene Transcription.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15611122","citation_count":45,"is_preprint":false},{"pmid":"21971700","id":"PMC_21971700","title":"Correlations among ERCC1, XPB, UBE2I, EGF, TAL2 and ILF3 revealed by gene signatures of histological subtypes of patients with epithelial ovarian cancer.","date":"2011","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/21971700","citation_count":42,"is_preprint":false},{"pmid":"11112409","id":"PMC_11112409","title":"Interaction of Daxx, a Fas binding protein, with sentrin and Ubc9.","date":"2000","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/11112409","citation_count":42,"is_preprint":false},{"pmid":"15666801","id":"PMC_15666801","title":"FHL2, UBC9, and PIAS1 are novel estrogen receptor alpha-interacting proteins.","date":"2004","source":"Endocrine research","url":"https://pubmed.ncbi.nlm.nih.gov/15666801","citation_count":41,"is_preprint":false},{"pmid":"23381475","id":"PMC_23381475","title":"Ubc9 promotes invasion and metastasis of lung cancer cells.","date":"2013","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/23381475","citation_count":39,"is_preprint":false},{"pmid":"38167292","id":"PMC_38167292","title":"Stabilization of Pin1 by USP34 promotes Ubc9 isomerization and protein sumoylation in glioma stem cells.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38167292","citation_count":37,"is_preprint":false},{"pmid":"16758298","id":"PMC_16758298","title":"Role of SUMO/Ubc9 in DNA damage repair and tumorigenesis.","date":"2006","source":"Journal of molecular histology","url":"https://pubmed.ncbi.nlm.nih.gov/16758298","citation_count":37,"is_preprint":false},{"pmid":"19944179","id":"PMC_19944179","title":"cDNA cloning and expression of Ubc9 in the developing embryo and ovary of Oriental river prawn, Macrobrachium nipponense.","date":"2009","source":"Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/19944179","citation_count":33,"is_preprint":false},{"pmid":"19358266","id":"PMC_19358266","title":"Common variants in the UBC9 gene encoding the SUMO-conjugating enzyme are associated with breast tumor grade.","date":"2009","source":"International journal of cancer","url":"https://pubmed.ncbi.nlm.nih.gov/19358266","citation_count":33,"is_preprint":false},{"pmid":"31704792","id":"PMC_31704792","title":"Loss of the E2 SUMO-conjugating enzyme Ube2i in oocytes during ovarian folliculogenesis causes infertility in mice.","date":"2019","source":"Development (Cambridge, England)","url":"https://pubmed.ncbi.nlm.nih.gov/31704792","citation_count":32,"is_preprint":false},{"pmid":"14765993","id":"PMC_14765993","title":"Ubc9 interacts with chicken ovalbumin upstream promoter-transcription factor I and represses receptor-dependent transcription.","date":"2004","source":"Journal of molecular endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/14765993","citation_count":31,"is_preprint":false},{"pmid":"32249212","id":"PMC_32249212","title":"SUMOylation of the transcription factor ZFHX3 at Lys-2806 requires SAE1, UBC9, and PIAS2 and enhances its stability and function in cell proliferation.","date":"2020","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/32249212","citation_count":31,"is_preprint":false},{"pmid":"19149481","id":"PMC_19149481","title":"Targeting the SUMO E2 conjugating enzyme Ubc9 interaction for anti-cancer drug design.","date":"2009","source":"Anti-cancer agents in medicinal chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/19149481","citation_count":31,"is_preprint":false},{"pmid":"24706591","id":"PMC_24706591","title":"The SUMO conjugating enzyme Ubc9 is required for inducing and maintaining stem cell pluripotency.","date":"2014","source":"Stem cells (Dayton, Ohio)","url":"https://pubmed.ncbi.nlm.nih.gov/24706591","citation_count":30,"is_preprint":false},{"pmid":"21344391","id":"PMC_21344391","title":"Ubc9 mediates nuclear localization and growth suppression of BRCA1 and BRCA1a proteins.","date":"2011","source":"Journal of cellular physiology","url":"https://pubmed.ncbi.nlm.nih.gov/21344391","citation_count":30,"is_preprint":false},{"pmid":"19640976","id":"PMC_19640976","title":"Human Ubc9 contributes to production of fully infectious human immunodeficiency virus type 1 virions.","date":"2009","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/19640976","citation_count":30,"is_preprint":false},{"pmid":"17709345","id":"PMC_17709345","title":"Ubc9 fusion-directed SUMOylation identifies constitutive and inducible SUMOylation.","date":"2007","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/17709345","citation_count":28,"is_preprint":false},{"pmid":"29472640","id":"PMC_29472640","title":"Ubc9 overexpression and SUMO1 deficiency blunt inflammation after intestinal ischemia/reperfusion.","date":"2018","source":"Laboratory investigation; a journal of technical methods and pathology","url":"https://pubmed.ncbi.nlm.nih.gov/29472640","citation_count":26,"is_preprint":false},{"pmid":"17698038","id":"PMC_17698038","title":"RAP80 interacts with the SUMO-conjugating enzyme UBC9 and is a novel target for sumoylation.","date":"2007","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/17698038","citation_count":25,"is_preprint":false},{"pmid":"23097446","id":"PMC_23097446","title":"SUMO-conjugating enzyme E2 UBC9 mediates viral immediate-early protein SUMOylation in crayfish to facilitate reproduction of white spot syndrome virus.","date":"2012","source":"Journal of virology","url":"https://pubmed.ncbi.nlm.nih.gov/23097446","citation_count":25,"is_preprint":false},{"pmid":"16631162","id":"PMC_16631162","title":"Ubc9 expression is essential for myotube formation in C2C12.","date":"2006","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/16631162","citation_count":25,"is_preprint":false},{"pmid":"18321803","id":"PMC_18321803","title":"Ubc9 promotes the stability of Smad4 and the nuclear accumulation of Smad1 in osteoblast-like Saos-2 cells.","date":"2008","source":"Bone","url":"https://pubmed.ncbi.nlm.nih.gov/18321803","citation_count":25,"is_preprint":false},{"pmid":"25311713","id":"PMC_25311713","title":"mGlu5 receptors regulate synaptic sumoylation via a transient PKC-dependent diffusional trapping of Ubc9 into spines.","date":"2014","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/25311713","citation_count":25,"is_preprint":false},{"pmid":"23470653","id":"PMC_23470653","title":"UBC9 regulates the stability of XBP1, a key transcription factor controlling the ER stress response.","date":"2013","source":"Cell structure and function","url":"https://pubmed.ncbi.nlm.nih.gov/23470653","citation_count":24,"is_preprint":false},{"pmid":"19760037","id":"PMC_19760037","title":"Polymorphisms in the UBC9 and PIAS3 genes of the SUMO-conjugating system and breast cancer risk.","date":"2009","source":"Breast cancer research and treatment","url":"https://pubmed.ncbi.nlm.nih.gov/19760037","citation_count":24,"is_preprint":false},{"pmid":"24395713","id":"PMC_24395713","title":"SUMO Ubc9 enzyme as a viral target.","date":"2014","source":"IUBMB life","url":"https://pubmed.ncbi.nlm.nih.gov/24395713","citation_count":23,"is_preprint":false},{"pmid":"32950589","id":"PMC_32950589","title":"Targeting UBC9-mediated protein hyper-SUMOylation in cystic cholangiocytes halts polycystic liver disease in experimental models.","date":"2020","source":"Journal of hepatology","url":"https://pubmed.ncbi.nlm.nih.gov/32950589","citation_count":23,"is_preprint":false},{"pmid":"28572537","id":"PMC_28572537","title":"Down-regulation of UBC9 increases the sensitivity of hepatocellular carcinoma to doxorubicin.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28572537","citation_count":23,"is_preprint":false},{"pmid":"28784659","id":"PMC_28784659","title":"Site-specific inhibition of the small ubiquitin-like modifier (SUMO)-conjugating enzyme Ubc9 selectively impairs SUMO chain formation.","date":"2017","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/28784659","citation_count":23,"is_preprint":false},{"pmid":"30828290","id":"PMC_30828290","title":"The SUMO-Conjugase Ubc9 Prevents the Degradation of the Dopamine Transporter, Enhancing Its Cell Surface Level and Dopamine Uptake.","date":"2019","source":"Frontiers in cellular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/30828290","citation_count":23,"is_preprint":false},{"pmid":"24531852","id":"PMC_24531852","title":"SUMO-conjugating enzyme UBC9 promotes proliferation and migration of fibroblast-like synoviocytes in rheumatoid arthritis.","date":"2014","source":"Inflammation","url":"https://pubmed.ncbi.nlm.nih.gov/24531852","citation_count":22,"is_preprint":false},{"pmid":"28314856","id":"PMC_28314856","title":"Ubc9 Is Required for Positive Selection and Late-Stage Maturation of Thymocytes.","date":"2017","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/28314856","citation_count":22,"is_preprint":false},{"pmid":"16782883","id":"PMC_16782883","title":"Distinct functional domains of Ubc9 dictate cell survival and resistance to genotoxic stress.","date":"2006","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16782883","citation_count":22,"is_preprint":false},{"pmid":"16566921","id":"PMC_16566921","title":"Regulation of bcl-2 expression by Ubc9.","date":"2006","source":"Experimental cell research","url":"https://pubmed.ncbi.nlm.nih.gov/16566921","citation_count":21,"is_preprint":false},{"pmid":"19765634","id":"PMC_19765634","title":"Ubc9 gene polymorphisms and late-onset Alzheimer's disease in the Korean population: a genetic association study.","date":"2009","source":"Neuroscience letters","url":"https://pubmed.ncbi.nlm.nih.gov/19765634","citation_count":21,"is_preprint":false},{"pmid":"30772377","id":"PMC_30772377","title":"UBC9 regulates cardiac sodium channel Nav1.5 ubiquitination, degradation and sodium current density.","date":"2019","source":"Journal of molecular and cellular cardiology","url":"https://pubmed.ncbi.nlm.nih.gov/30772377","citation_count":21,"is_preprint":false},{"pmid":"25586181","id":"PMC_25586181","title":"UBC9-dependent association between calnexin and protein tyrosine phosphatase 1B (PTP1B) at the endoplasmic reticulum.","date":"2015","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/25586181","citation_count":20,"is_preprint":false},{"pmid":"16275321","id":"PMC_16275321","title":"Purification and activity assays for Ubc9, the ubiquitin-conjugating enzyme for the small ubiquitin-like modifier SUMO.","date":"2005","source":"Methods in enzymology","url":"https://pubmed.ncbi.nlm.nih.gov/16275321","citation_count":20,"is_preprint":false},{"pmid":"18211895","id":"PMC_18211895","title":"MEL-18 interacts with HSF2 and the SUMO E2 UBC9 to inhibit HSF2 sumoylation.","date":"2008","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/18211895","citation_count":20,"is_preprint":false},{"pmid":"33244139","id":"PMC_33244139","title":"UBC9 coordinates inflammation affecting development of bladder cancer.","date":"2020","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/33244139","citation_count":19,"is_preprint":false},{"pmid":"35237717","id":"PMC_35237717","title":"Site-Specific Protein Ubiquitylation Using an Engineered, Chimeric E1 Activating Enzyme and E2 SUMO Conjugating Enzyme Ubc9.","date":"2022","source":"ACS central science","url":"https://pubmed.ncbi.nlm.nih.gov/35237717","citation_count":19,"is_preprint":false},{"pmid":"24961570","id":"PMC_24961570","title":"The Role of SUMO-Conjugating Enzyme Ubc9 in the Neuroprotection of Isoflurane Preconditioning Against Ischemic Neuronal Injury.","date":"2014","source":"Molecular neurobiology","url":"https://pubmed.ncbi.nlm.nih.gov/24961570","citation_count":19,"is_preprint":false},{"pmid":"12200128","id":"PMC_12200128","title":"Interaction of the developmental regulator SALL1 with UBE2I and SUMO-1.","date":"2002","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/12200128","citation_count":18,"is_preprint":false},{"pmid":"18655774","id":"PMC_18655774","title":"Modulation of PLAGL2 transactivation activity by Ubc9 co-activation not SUMOylation.","date":"2008","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/18655774","citation_count":18,"is_preprint":false},{"pmid":"20881252","id":"PMC_20881252","title":"Role of UBC9 in the regulation of the adipogenic program in 3T3-L1 adipocytes.","date":"2010","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/20881252","citation_count":18,"is_preprint":false},{"pmid":"23507627","id":"PMC_23507627","title":"Cloning, genomic structure and expression analysis of ubc9 in the course of development in the half-smooth tongue sole (Cynoglossus semilaevis).","date":"2013","source":"Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/23507627","citation_count":18,"is_preprint":false},{"pmid":"21467194","id":"PMC_21467194","title":"Coactivation of SF-1-mediated transcription of steroidogenic enzymes by Ubc9 and PIAS1.","date":"2011","source":"Endocrinology","url":"https://pubmed.ncbi.nlm.nih.gov/21467194","citation_count":18,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":50908,"output_tokens":13136,"usd":0.174882,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":24853,"output_tokens":6833,"usd":0.147545,"stage2_stop_reason":"end_turn"},"total_usd":0.322427,"stage1_batch_id":"msgbatch_017qqVz33Ga63SCDwzb35XPb","stage2_batch_id":"msgbatch_01Scr2Ei9x4HJMiRGxwrmvLK","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 1998,\n      \"finding\": \"UBC9/UBE2I functions as the E2 SUMO-conjugating enzyme, forming thioester intermediates with SMT3 (yeast) and SUMO-1 (mammalian) analogous to ubiquitin-conjugating enzymes; yeast UBC9 is required for SMT3 conjugation in vivo.\",\n      \"method\": \"In vitro thioester formation assay, in vivo complementation in yeast ubc9 mutant\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro biochemical reconstitution of thioester intermediates plus in vivo genetic complementation, replicated across multiple labs\",\n      \"pmids\": [\"9435231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"SAE1/SAE2 (E1) and Ubc9 (E2) catalyze formation of polymeric SUMO-2 and SUMO-3 chains on protein substrates in vitro; SUMO-2 chains are also detected in vivo. SUMO-1 lacks the consensus ψKXE site and cannot form such chains.\",\n      \"method\": \"In vitro reconstitution of SUMO chain formation; in vivo detection by immunoblot\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution plus in vivo validation, foundational mechanistic paper\",\n      \"pmids\": [\"11451954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"An N-terminal region of Ubc9 (residues including R13, K14, R17, K18) mediates noncovalent interaction with SUMO-1; mutations at this site (R13A/K14A, R17A/K18A) reduce transfer of SUMO-1 from E1 to E2 without abolishing substrate recognition or SUMO transfer from E2 to target.\",\n      \"method\": \"Site-directed mutagenesis, isothermal titration calorimetry, in vitro SUMO conjugation assay, NMR chemical shift perturbation\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — mutagenesis combined with ITC and in vitro reconstitution, multiple orthogonal methods in one study\",\n      \"pmids\": [\"12924945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"NMR chemical shift perturbation identified the beta-sheet surface of Ubc9 as the binding site for the RanBP2/Nup358 E3 SUMO ligase; this interaction is distinct from classical ubiquitin E2–E3 interactions and is required for SUMO-2 (but not SUMO-1) conjugation to Sp100 and PML. RanBP2 contains a SUMO-1-specific binding site, enabling paralog-selective conjugation.\",\n      \"method\": \"NMR chemical shift perturbation, site-directed mutagenesis, in vitro SUMO conjugation assays\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — NMR structure-function combined with mutagenesis and biochemical assays, multiple orthogonal methods\",\n      \"pmids\": [\"15608651\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Crystal structure of a four-protein complex (Ubc9, Nup358/RanBP2 E3 ligase domain IR1-M, SUMO-1 conjugated to RanGAP1 C-terminal domain) at 3.0 Å reveals that Nup358/RanBP2 acts as an E3 by binding both SUMO and Ubc9 to position the SUMO–E2 thioester for optimal orientation during conjugation.\",\n      \"method\": \"X-ray crystallography (3.0 Å), biochemical and kinetic assays with additional substrates\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with kinetic validation, rigorous mechanistic study\",\n      \"pmids\": [\"15931224\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Ubc9 directly purifies as an active SUMO E2: it forms E2~SUMO thioester intermediates and catalyzes SUMO conjugation to consensus ψKXE motifs in substrate proteins in vitro using only E1, Ubc9, mature SUMO, and ATP.\",\n      \"method\": \"In vitro reconstitution, E2 thioester formation assay, single-turnover and multiple-turnover conjugation assays\",\n      \"journal\": \"Methods in enzymology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — detailed in vitro biochemical reconstitution with defined components\",\n      \"pmids\": [\"16275321\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In budding yeast, distinct functional domains of Ubc9 are required for cell viability versus resistance to DNA damage: swapping domains affecting substrate binding, RanBP2 E3 interaction, and E1/SUMO binding had distinct effects; the activities of E3 ligases Siz1 and Siz2 in genotoxic stress responses were distinguished. Crystal structure of yeast Ubc9 at 1.75 Å resolved these domain functions.\",\n      \"method\": \"X-ray crystallography (1.75 Å), human/yeast chimera construction, yeast genetic complementation, DNA damage sensitivity assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with chimera genetics and functional assays\",\n      \"pmids\": [\"16782883\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ubc9 forms a noncovalent complex with SUMO-1 through a surface far from the E2 active site; crystal structure at 2.4 Å shows this interface is conserved with ubiquitin pathway E2–Ubl interactions. Biochemically, this noncovalent interface is less important for E1 activation or di-SUMO-2 formation but important for E3 interactions and for poly-SUMO chain formation beyond two SUMO units.\",\n      \"method\": \"X-ray crystallography (2.4 Å), in vitro SUMO chain formation assays, E1 activation assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure with biochemical dissection of specific pathway steps\",\n      \"pmids\": [\"17466333\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"The noncovalent interaction between Ubc9 and SUMO (via the 'backside' binding site far from the active site) promotes formation of short SUMO chains on substrates Sp100 and HDAC4; crystal structure of the noncovalent Ubc9–SUMO1 complex reveals structural analogy to the Mms2–Ubc13 ubiquitin chain-forming mechanism.\",\n      \"method\": \"X-ray crystallography, in vitro SUMO chain formation assays, MS identification of chain linkages\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with in vitro reconstitution and mass spectrometry\",\n      \"pmids\": [\"17491593\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Auto-sumoylation of Ubc9 at Lys14 regulates target discrimination: sumoylated Ubc9 impairs activity toward RanGAP1 and strongly activates sumoylation of Sp100 via a SUMO-interacting motif (SIM) in Sp100 that creates an additional interface with the SUMO conjugated to the E2. Crystal structure of sumoylated Ubc9 demonstrates the new binding interface.\",\n      \"method\": \"Crystal structure of sumoylated Ubc9, in vitro SUMO conjugation assays with multiple substrates, SIM mutagenesis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with biochemical functional assays and mutagenesis\",\n      \"pmids\": [\"18691969\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Crystal structure of Ubc9 in complex with Rad60's SUMO-like domain 2 (SLD2) reveals that Ubc9:SLD2 and Ubc9:SUMO noncovalent complexes are structurally analogous. Disrupting Ubc9:SLD2 selectively impairs Nse2 E3 ligase-dependent DNA repair, while disrupting Ubc9:SUMO noncovalent interaction impairs global sumoylation and SUMO chain formation via Pli1 E3 ligase.\",\n      \"method\": \"X-ray crystallography, site-directed mutagenesis, yeast genetic epistasis, in vivo sumoylation assays\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure combined with mutagenesis and genetic pathway dissection\",\n      \"pmids\": [\"21444718\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"CDK1/cyclin B phosphorylates Ubc9 at Ser71 in vitro; phosphorylated Ubc9 shows increased SUMOylation activity and elevated Ubc9–SUMO1 thioester accumulation. CDK2/cyclin E and other cell cycle kinases tested did not show this activity.\",\n      \"method\": \"In vitro kinase assay, in vitro SUMO conjugation assay, site-directed mutagenesis (S71A)\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution with mutagenesis but single lab, single study\",\n      \"pmids\": [\"22509284\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Acetylation of Ubc9 at Lys65 selectively downregulates sumoylation of substrates with negatively charged amino acid-dependent sumoylation motifs (NDSM), such as CBP and Elk-1, by attenuating Ubc9 binding to NDSM substrates, without affecting substrates with core ψKXE motif alone. SIRT1 deacetylates Ubc9 K65 under hypoxia, linking this modification to the hypoxia response.\",\n      \"method\": \"In vitro SUMO conjugation assays, mass spectrometry identification of acetylation site, mutagenesis, siRNA knockdown of SIRT1, reporter assays\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with mutagenesis and MS, mechanistic link to SIRT1/hypoxia pathway, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"23395904\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"In S. cerevisiae, sumoylation of Ubc9 at Lys153 (Ubc9*SUMO) converts it from an active enzyme into a catalytic cofactor: Ubc9*SUMO is severely impaired in classical SUMO conjugation activity but promotes SUMO chain assembly by cooperating with charged Ubc9 (Ubc9~SUMO) through noncovalent backside SUMO binding, positioning donor SUMO for optimal transfer. A sumoylation-deficient mutant shows reduced meiotic SUMO conjugates and abrogated synaptonemal complex formation.\",\n      \"method\": \"In vitro SUMO conjugation/chain formation assays, site-directed mutagenesis, yeast genetics (meiotic phenotype), biochemical reconstitution\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis, in vivo genetic phenotype, mechanistic dissection of catalytic vs. cofactor roles\",\n      \"pmids\": [\"23644018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Akt directly phosphorylates Ubc9 at Thr35; this phosphorylation promotes Ubc9 thioester bond formation with SUMO1, increasing global SUMOylation and substrate-specific SUMOylation (e.g., STAT1, CREB). Akt also phosphorylates SUMO1 at Thr76, stabilizing SUMO1 protein.\",\n      \"method\": \"In vitro kinase assay, thioester formation assay, site-directed mutagenesis (T35A), co-immunoprecipitation, reporter assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro reconstitution with mutagenesis, single lab, pleiotropic claims\",\n      \"pmids\": [\"25867063\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"High-affinity SUMO2 variants (SUBINs) engineered to bind the backside binding site of Ubc9 selectively inhibit poly-SUMO chain formation without impairing mono-SUMOylation, demonstrating that these two activities use distinct surfaces of Ubc9. In cells, SUBINs largely prevent heat shock-triggered poly-SUMOylation and abrogate arsenic-induced PML degradation.\",\n      \"method\": \"Phage display protein engineering, in vitro SUMO chain formation assays, cellular heat shock and arsenic treatment assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with engineered inhibitors, cellular validation, multiple orthogonal methods\",\n      \"pmids\": [\"28784659\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Pin1 isomerizes Ubc9 in a CDK1-phosphorylation-dependent manner (CDK1-mediated phosphorylation of Ubc9 is required), upregulating Ubc9 thioester formation with SUMO1 and driving SUMO1-modified hypersumoylation in glioma stem cells. Pin1 stability is maintained by USP34-mediated deubiquitination, facilitated by Plk1-mediated phosphorylation of Pin1.\",\n      \"method\": \"Co-immunoprecipitation, in vitro thioester formation assay, site-directed mutagenesis (CDK1 phosphosite), inhibitor studies (sulfopin, RO3306), in vivo tumor model\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, biochemical assays, in vivo tumor model, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"38167292\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human UBE2I (HsUbc9) interacts with Rad51 recombination protein in a yeast two-hybrid assay, and mouse MmUbc9 protein localizes to synaptonemal complexes in spermatocytes, suggesting a regulatory role in meiosis.\",\n      \"method\": \"Yeast two-hybrid, immunolocalization in mouse spermatocytes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — yeast two-hybrid interaction with localization, no direct functional mechanistic follow-up\",\n      \"pmids\": [\"8610150\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"UBE2I interacts with RAD52, RAD51, p53, and UBL1 (SUMO-1) in yeast two-hybrid assays; these interactions are UBE2I-specific (RAD6/UBC2 does not interact). The RAD52 interaction is mediated by RAD52's self-association region.\",\n      \"method\": \"Yeast two-hybrid system\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single method (yeast two-hybrid), no biochemical validation\",\n      \"pmids\": [\"8921390\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1996,\n      \"finding\": \"Human UBC9 (UBE2I) functionally complements a S. cerevisiae ubc9 temperature-sensitive mutant, rescuing cell cycle progression defects, demonstrating structural and functional conservation.\",\n      \"method\": \"Yeast genetic complementation\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic complementation assay demonstrating functional conservation, replicated across multiple 1996 papers\",\n      \"pmids\": [\"8668529\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Ubc9 interacts with the androgen receptor (AR) hinge region containing the nuclear localization signal and enhances AR-dependent transcription; a C93S catalytic mutant of Ubc9 that cannot form SUMO-1 thioester still stimulates AR-dependent transactivation, indicating a SUMO-conjugation-independent coregulatory function.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation in COS-1 cells, transient transfection reporter assays, C93S mutagenesis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with active-site mutant to separate conjugation from coactivation, single lab\",\n      \"pmids\": [\"10383460\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The IR1+2 domain of RanBP2/Nup358 binds Ubc9 with high affinity in vitro and in vivo; when overexpressed in COS-7 cells, IR1+2 sequesters ~90% of nuclear Ubc9 to the cytoplasm, causing mislocalization of SUMO-1, SUMO-2/3, PML nuclear body enlargement, and cytoplasmic mislocalization of Rad51 with failure to form Rad51 DNA-damage foci, implicating nuclear Ubc9 in Rad51-mediated homologous recombination.\",\n      \"method\": \"GST pulldown, co-immunoprecipitation, GFP-IR1+2 overexpression with immunofluorescence, DNA damage assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assays combined with subcellular localization experiments and functional consequence (loss of Rad51 foci), single lab\",\n      \"pmids\": [\"11709548\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"UBC9 interacts with STRA13 in mammalian cells and promotes its ubiquitin-dependent proteasomal degradation; co-expression of STRA13 and UBC9 leads to increased pSTRA13 ubiquitination, and proteasome inhibitor blocks this degradation.\",\n      \"method\": \"Yeast two-hybrid, co-immunoprecipitation in mammalian cells, proteasome inhibitor treatment, ubiquitination assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP combined with proteasome inhibitor and ubiquitination assay, though unusual for Ubc9 to directly promote ubiquitination; single lab\",\n      \"pmids\": [\"11278694\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"siRNA-mediated knockdown of Ubc9 in HeLa cells reduces endogenous Smad4 levels and intranuclear Smad4 accumulation; SUMO-1 overexpression protects Smad4 from ubiquitin-dependent degradation by competing for the same modification site, leading to enhanced TGF-β transcriptional and growth-inhibitory responses.\",\n      \"method\": \"siRNA knockdown, SUMO-1 overexpression, subcellular fractionation, half-life analysis of Smad4 mutants, reporter assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with mechanistic follow-up comparing sumoylation/ubiquitination competition, single lab\",\n      \"pmids\": [\"12813045\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"In budding yeast, Ubc9 and Smt3 (SUMO) are required for efficient APC/C-mediated proteolysis: temperature-sensitive ubc9-2 and smt3-331 mutants show delayed degradation of securin Pds1 and cyclin Clb2 during mitosis, and are defective in chromosome segregation, while proteolysis of non-APC/C substrates is unaffected.\",\n      \"method\": \"Yeast genetics (temperature-sensitive mutants), cyclin/securin degradation assays, cell cycle analysis, chromosome segregation assays\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with temporal substrate degradation assays, single lab\",\n      \"pmids\": [\"14982631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In S. cerevisiae, Ubc9 and Mms21 SUMO ligase act in concert with Sgs1 helicase to resolve X-shaped cruciform structures at damaged replication forks; ubc9 mutants show Rad51-dependent accumulation of cruciform structures during replication of damaged templates. This SUMOylation function is distinct from the Siz1/PCNA/Srs2 pathway.\",\n      \"method\": \"Yeast genetics (ubc9 mutant), 2D gel electrophoresis to detect cruciform structures, epistasis analysis with siz1, srs2, pcna, sgs1, top3 mutants\",\n      \"journal\": \"Cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — rigorous epistasis analysis with molecular readout (2D gel), placed Ubc9 in a specific pathway distinct from Siz1/PCNA\",\n      \"pmids\": [\"17081974\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"In zebrafish, reduction of Ubc9 activity (dominant-negative expression or antisense knockdown) causes defects in G2/M transition and mitotic progression, resulting in cells with 4n or 8n DNA content and fewer cells in mitosis in cartilage/eye tissues, without equivalently increasing apoptosis.\",\n      \"method\": \"Dominant-negative expression, antisense morpholino knockdown, FACS analysis, BrdU incorporation, mitotic marker staining in zebrafish embryos\",\n      \"journal\": \"Molecular biology of the cell\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo loss-of-function in vertebrate model with cell cycle readouts, single lab\",\n      \"pmids\": [\"17035631\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"Ubc9 regulates GLUT4 stability and targeting to the insulin-responsive GLUT4 storage compartment (GSC) in 3T3-L1 adipocytes; overexpression inhibits GLUT4 degradation and promotes GSC targeting, increasing insulin-responsive glucose transport. A catalytically inactive mutant Ubc9-C93A produces the same effects, indicating SUMO-conjugation-independent regulation of GLUT4.\",\n      \"method\": \"Adenoviral overexpression, siRNA knockdown, glucose transport assay, subcellular fractionation, catalytic mutant (C93A)\",\n      \"journal\": \"Diabetes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with catalytic mutant to dissect mechanism, single lab\",\n      \"pmids\": [\"17536066\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"UBE2I localizes to nuclear speckles (colocalizing with SFRS2/SC35) in mouse oocytes; overexpression of either wild-type or catalytically inactive UBE2I increases BrUTP incorporation (transcription), demonstrating that transcriptional activation by UBE2I in oocytes is independent of its SUMO-conjugating activity.\",\n      \"method\": \"Immunocytochemistry, microinjection/overexpression of WT and catalytic mutant, BrUTP incorporation assay\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct localization with functional readout, catalytic mutant used, single lab\",\n      \"pmids\": [\"18703419\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Ubc9 interacts with HIV-1 Gag protein and colocalizes at perinuclear puncta; Ubc9 knockdown reduces virion infectivity 8–10-fold, associated with decreased cell-associated Env glycoprotein stability and altered Env incorporation into virions, without affecting Gag assembly or processing. The catalytic mutant Ubc9-C93A suggests SUMO-conjugating activity may not be required for this function.\",\n      \"method\": \"RNAi knockdown, colocalization imaging, virion infectivity assay, Env stability assay, catalytic mutant expression\",\n      \"journal\": \"Journal of virology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RNAi with functional readout and mechanistic dissection using catalytic mutant, single lab\",\n      \"pmids\": [\"19640976\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"UBC9 specifically binds the leucine zipper motif of spliced XBP1 (pXBP1(S)) and increases its protein stability; UBC9 knockdown reduces pXBP1(S) levels and ER stress-induced transcription. A SUMO-conjugating-inactive UBC9 mutant equally stabilizes pXBP1(S), indicating SUMOylation-independent stabilization.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown, reporter assay, catalytic mutant (SUMO-inactive UBC9)\",\n      \"journal\": \"Cell structure and function\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding with catalytic mutant dissecting SUMOylation independence, single lab\",\n      \"pmids\": [\"23470653\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Synaptic diffusion of Ubc9 in hippocampal neurons is regulated by mGlu5R-dependent signaling: activation of mGlu5R increases Ubc9 synaptic residency time via a Gαq/PLC/Ca2+/PKC cascade, promoting transient PKC phosphorylation-dependent synaptic trapping of Ubc9 and consequent modulation of synaptic sumoylation.\",\n      \"method\": \"Restricted photobleaching/photoconversion (FRAP/photoconversion) of individual hippocampal spines, pharmacological receptor activation, PKC inhibitor studies\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with FRAP/photoconversion with pharmacological pathway dissection, novel mechanism, single lab but rigorous\",\n      \"pmids\": [\"25311713\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"UBC9 overexpression in cardiomyocytes increases SUMOylation and upregulates autophagic flux; in a proteotoxic model (CryAB-R120G), UBC9 overexpression reduces aggregate formation, decreases fibrosis and hypertrophy, and improves cardiac function and survival, demonstrating that UBC9-mediated SUMOylation promotes cardiac autophagy and protein quality control.\",\n      \"method\": \"Adenoviral overexpression and siRNA knockdown in neonatal rat cardiomyocytes, transgenic mouse model, autophagic flux assays, cardiac function measurements\",\n      \"journal\": \"Circulation research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function in vitro and in vivo, mechanistic link to autophagy pathway, single lab\",\n      \"pmids\": [\"27142163\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"DNA damage induces nuclear accumulation of UBC9, which SUMOylates lamin A/C; this SUMOylation is required for the interaction between autophagy protein LC3 and lamin A/C, which is required for nucleophagy (degradation of nuclear lamin A/C and leaked nuclear DNA). UBC9 knockdown prevents lamin A/C SUMOylation and attenuates LC3–lamin A/C interaction and nucleophagy.\",\n      \"method\": \"siRNA knockdown of UBC9, co-immunoprecipitation, immunofluorescence, subcellular fractionation\",\n      \"journal\": \"Journal of experimental & clinical cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with co-IP and colocalization showing mechanistic pathway, single lab\",\n      \"pmids\": [\"30744690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UBC9 SUMOylates STAT4 at Lys350 in macrophages; mutation K350R enhances STAT4 nuclear translocation and stability, facilitating proinflammatory macrophage activation. Macrophage-specific Ubc9 deficiency augments CD8+ T cell-mediated antitumor response in prostate cancer.\",\n      \"method\": \"Biochemical/molecular analysis of SUMO modification site (site-directed mutagenesis K350R), co-immunoprecipitation, macrophage-specific knockout mouse model, tumor growth assays\",\n      \"journal\": \"The Journal of clinical investigation\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — mutagenesis of SUMO acceptor site with in vivo KO model, single lab\",\n      \"pmids\": [\"36626227\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ubc9-mediated SUMOylation of IRF4 enhances its nuclear localization and stability, thereby transcribing IL-4 and arginase 1 to promote macrophage M2 polarization; macrophage-specific Ubc9 knockout impairs M2 polarization and exacerbates streptozotocin-induced diabetes.\",\n      \"method\": \"Macrophage-specific knockout mouse (LyzM-Cre-Ubc9fl/fl), co-immunoprecipitation, subcellular fractionation, gene expression analysis\",\n      \"journal\": \"Cell death & disease\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell type-specific knockout with biochemical identification of SUMO substrate and functional readout, single lab\",\n      \"pmids\": [\"31767832\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ubc9/SUMO-conjugase overexpression induces SUMO1-dependent DAT SUMOylation, reduces DAT ubiquitination and lysosomal degradation, enhances DAT plasma membrane steady-state level, and increases dopamine uptake capacity; Ubc9 knockdown has the opposite effects.\",\n      \"method\": \"Confocal microscopy, FRET, Western blot, RNAi knockdown, dopamine uptake assay\",\n      \"journal\": \"Frontiers in cellular neuroscience\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — gain- and loss-of-function with functional readout, multiple imaging methods, single lab\",\n      \"pmids\": [\"30828290\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"UBC9 interacts with Nedd4-2 E3 ubiquitin ligase (by co-immunoprecipitation) and promotes ubiquitination and proteasomal degradation of Nav1.5 (cardiac sodium channel); UBC9 overexpression decreases Nav1.5 expression and reduces sodium current densities, while UBC9 knockdown has the opposite effect. The C93S catalytic mutant equally regulates Nav1.5, indicating a SUMO-conjugating-independent mechanism.\",\n      \"method\": \"Co-immunoprecipitation, overexpression/knockdown in HEK293 and cardiomyocytes, patch clamp electrophysiology, proteasome inhibitor (MG132), catalytic mutant (C93S)\",\n      \"journal\": \"Journal of molecular and cellular cardiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with functional electrophysiology and catalytic mutant dissection, single lab\",\n      \"pmids\": [\"30772377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Ubc9 interacts with bovine papillomavirus E1 replication protein both in vitro and in vivo; Ubc9 catalyzes covalent SUMO-1 conjugation to E1. An E1 mutant unable to bind Ubc9 shows impaired intranuclear distribution but normal stability, suggesting sumoylation is important for E1 nuclear subdomain localization.\",\n      \"method\": \"Yeast two-hybrid, in vitro binding, in vivo co-immunoprecipitation, in vitro SUMO-1 conjugation assay, mutational mapping\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro binding and SUMO conjugation assay with functional mutant analysis, single lab\",\n      \"pmids\": [\"10871618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Loss of Ubc9 in chicken DT40 cells (conditional knockout) causes cell death with increased multinucleated cells (defect in cytokinesis) and apoptosis, rather than the G2/M block seen in yeast ubc9 mutants, demonstrating distinct essential roles of SUMO conjugation in higher eukaryotes.\",\n      \"method\": \"Conditional gene knockout (tetracycline-repressible transgene), FACS cell cycle analysis, microscopic analysis of nuclear morphology\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO with defined cellular phenotype, single lab\",\n      \"pmids\": [\"12413887\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Inducible knockout of Ubc9 in adult mouse intestinal epithelium causes rapid depletion of intestinal stem cells, loss of the proliferative compartment, disruption of enterocyte polarity (nucleus positioning and actin organization), and detachment from basal lamina. Keratin 8 was identified as a SUMO substrate in intestinal epithelial cells.\",\n      \"method\": \"Inducible conditional knockout mouse (4-OHT), histology, immunofluorescence, in vitro SUMO conjugation assay for keratin 8\",\n      \"journal\": \"Gastroenterology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — conditional KO in adult mice with precise phenotypic readouts plus substrate identification, rigorous in vivo study\",\n      \"pmids\": [\"20951138\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Ubc9 knockdown stimulates apoptosis in embryonic stem cells (ESCs) but not MEFs; Ubc9 is required for reprogramming MEFs to iPS cells (knockdown dramatically inhibits reprogramming); Ubc9 knockdown decreases expression of pluripotency markers Nanog, Klf4, Oct4, and Sox2 in ESCs.\",\n      \"method\": \"siRNA knockdown, apoptosis assays, reprogramming efficiency measurement, qRT-PCR for pluripotency markers\",\n      \"journal\": \"Stem cells (Dayton, Ohio)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with specific phenotypic readouts in defined cell types, single lab\",\n      \"pmids\": [\"24706591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"p14ARF interacts with Ubc9 and enhances SUMO-1 modification of its binding partners (hdm2, E2F-1, HIF-1α, TBP-1, p120E4F); melanoma-associated p14ARF mutations abrogate this sumoylation-enhancing activity, suggesting p14ARF acts as a SUMO E3-like factor through Ubc9.\",\n      \"method\": \"Co-immunoprecipitation, in vivo sumoylation assays, mutagenesis of p14ARF cancer-associated mutations\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — co-IP with in vivo sumoylation assays, replicated across multiple substrates, but no in vitro reconstitution\",\n      \"pmids\": [\"15876874\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Ubc9 directly binds CRMP2 with low micromolar affinity (measured by microscale thermophoresis and AlphaLISA); disrupting this interaction with a tat-conjugated CRMP2 SUMOylation motif peptide (t-CSM) decreases CRMP2 SUMOylation, reduces NaV1.7 surface trafficking and sodium currents in sensory neurons, and reverses mechanical and thermal hypersensitivity in a spinal nerve injury model.\",\n      \"method\": \"Microscale thermophoresis, AlphaLISA binding assay, peptide inhibitor, patch clamp electrophysiology, in vivo neuropathic pain model\",\n      \"journal\": \"Pain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biophysical binding measurements with functional in vitro and in vivo readouts, single lab\",\n      \"pmids\": [\"29847471\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"MEL-18 (polycomb protein) interacts with both HSF2 and UBC9; MEL-18 overexpression decreases HSF2 sumoylation and broad cellular protein sumoylation, while MEL-18 knockdown increases them. MEL-18 inhibits UBC9's ability to transfer SUMO to target proteins, functioning as an anti-E3 inhibitor of UBC9 activity. MEL-18 binding to HSF2 decreases during mitosis, correlating with increased mitotic HSF2 sumoylation.\",\n      \"method\": \"Co-immunoprecipitation, RNAi knockdown, overexpression, in vitro SUMO transfer assay\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP with in vitro SUMO transfer assay and gain/loss-of-function, single lab\",\n      \"pmids\": [\"18211895\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"A chimeric E1 enzyme (containing the Ub fold domain of SUMO E1 and remaining domains of Ub E1) activates and loads native ubiquitin onto Ubc9, enabling Ubc9-mediated site-specific ubiquitylation of target proteins bearing a short peptide tag (LACE system) in vitro and in E. coli.\",\n      \"method\": \"Protein engineering, directed evolution of chimeric E1, in vitro ubiquitylation assay, E. coli co-expression\",\n      \"journal\": \"ACS central science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro biochemical reconstitution with engineered enzyme, demonstrates Ubc9 active site can accommodate Ub via modified E1 loading\",\n      \"pmids\": [\"35237717\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Beta cell-specific knockout of Ubc9 in mice causes loss of beta cell mass, increased reactive oxygen species, and diabetes; SUMOylation of NRF2 by Ubc9 promotes NRF2 nuclear expression and transcriptional activity, thereby preventing ROS accumulation. Conversely, Ubc9 overexpression preserves normal blood glucose but impairs insulin secretion.\",\n      \"method\": \"Conditional knockout and transgenic mouse models (beta cell-specific), ROS measurement, NRF2 subcellular fractionation, immunoprecipitation for SUMOylation\",\n      \"journal\": \"Diabetologia\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — conditional KO and transgenic models with defined cellular and molecular phenotypes, single lab\",\n      \"pmids\": [\"29299635\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Loss of oocyte-specific Ubc9 in mice causes female infertility with defects in primordial follicle pool stability, folliculogenesis, ovulation and meiosis, and impairs expression of NOBOX and its target genes, demonstrating that SUMOylation in oocytes regulates both oocyte development and communication with granulosa cells.\",\n      \"method\": \"Oocyte-specific conditional knockout mouse, histology, transcriptomic profiling of ovaries\",\n      \"journal\": \"Development (Cambridge, England)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cell type-specific conditional KO with transcriptomic analysis, single lab\",\n      \"pmids\": [\"31704792\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"siRNA-mediated Ubc9 knockdown severely compromises C2C12 myoblast terminal differentiation and myotube formation without affecting expression, localization, or activation of MyoD or myogenin, placing SUMO-dependent targets downstream of these regulators as required for myogenesis.\",\n      \"method\": \"siRNA knockdown, Oil Red O staining, immunofluorescence, Western blotting for myogenic factors\",\n      \"journal\": \"Experimental cell research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — loss-of-function with epistatic placement (downstream of MyoD/myogenin), single lab\",\n      \"pmids\": [\"16631162\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"UBC9 is physiologically targeted for degradation by autophagy in human cells; HPV E6/E7 oncoproteins inhibit autophagosome-lysosome fusion, blocking autophagic degradation of UBC9 and leading to p53-dependent UBC9 accumulation during viral transformation.\",\n      \"method\": \"Ultrastructural analysis (EM), pharmacological and genetic autophagy inhibition/activation, HPV E6/E7 expression, p53 manipulation\",\n      \"journal\": \"PLoS pathogens\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal approaches (EM, pharmacology, genetics) identifying autophagy as UBC9 degradation pathway, single lab\",\n      \"pmids\": [\"28253371\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"UBC9 interacts with the cytoplasmic domain of calnexin (an ER membrane chaperone) and SUMOylates it; this interaction modulates calnexin's association with PTP1B, forming UBC9-dependent calnexin–PTP1B complexes at the ER membrane, linking SUMOylation to ER protein quality control and insulin/leptin signaling regulation.\",\n      \"method\": \"Co-immunoprecipitation, GST pulldown, in vitro and in vivo SUMO modification assay, immunofluorescence colocalization\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and in vitro SUMOylation with functional consequence of ternary complex, single lab\",\n      \"pmids\": [\"25586181\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Zebrafish Ubc9 interacts with and SUMOylates DeltaNp63alpha; Ubc9-mediated sumoylation (together with Nedd4-mediated ubiquitination) destabilizes DeltaNp63alpha protein on the dorsal side of the embryo. Mutant DeltaNp63alpha unable to bind Ubc9 is stabilized, leading to more widespread neural repression.\",\n      \"method\": \"Yeast two-hybrid, in vivo sumoylation assay in HEK293 and zebrafish embryos, mutational analysis, rescue experiments in zebrafish\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo sumoylation assays with mutagenesis and in vivo functional phenotype, single lab\",\n      \"pmids\": [\"15908775\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"Ubc9 mediates nuclear localization of BRCA1 and BRCA1a; siRNA knockdown of Ubc9 in MCF-7 cells causes enhanced cytoplasmic localization of BRCA1 and exclusive cytoplasmic retention of BRCA1a/BRCA1b, which is associated with loss of growth suppression and ER-α repression activities of BRCA1.\",\n      \"method\": \"Live cell imaging (YFP/GFP/RFP-tagged BRCA1), siRNA knockdown, colony formation assay\",\n      \"journal\": \"Journal of cellular physiology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — live imaging with siRNA knockdown linking localization to function, single lab\",\n      \"pmids\": [\"21344391\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"FOSL1 promotes UBC9-dependent SUMOylation of CYLD, inducing K63-linked polyubiquitination of NF-κB intermediaries and NF-κB activation, which drives proneural-to-mesenchymal transition in glioblastoma stem cells.\",\n      \"method\": \"Co-immunoprecipitation, SUMO modification assay, NF-κB reporter, FOSL1 knockdown/overexpression, in vivo tumor model\",\n      \"journal\": \"Molecular therapy : the journal of the American Society of Gene Therapy\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP and sumoylation assays with in vivo validation, pathway placed with mechanistic detail, single lab\",\n      \"pmids\": [\"35351656\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBE2I (UBC9) is the sole E2 SUMO-conjugating enzyme in mammalian cells: it receives activated SUMO from the SAE1/SAE2 E1 heterodimer via a catalytic Cys93 thioester intermediate, directly recognizes consensus ψKXE sumoylation motifs in substrates, and transfers SUMO-1, -2, or -3 to target lysines either alone or in cooperation with E3 ligases (e.g., RanBP2/Nup358, PIAS family); its noncovalent backside interaction with SUMO promotes poly-SUMO chain formation, while autosumoylation at Lys14 and post-translational modifications of Ubc9 itself (phosphorylation by CDK1 at Ser71, acetylation at Lys65 reversed by SIRT1, prolyl isomerization by Pin1) dynamically regulate its activity and substrate selectivity; beyond its enzymatic role, Ubc9 acts as a SUMO-conjugation-independent coactivator/corepressor for multiple nuclear receptors and transcription factors, and is required for cell viability, cytokinesis, G2/M progression, DNA repair, intestinal stem cell maintenance, cardiomyocyte protein quality control, and numerous other cellular processes.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBE2I (UBC9) is the E2 SUMO-conjugating enzyme that drives protein sumoylation across eukaryotes, receiving activated SUMO from the SAE1/SAE2 E1 heterodimer via a Cys93 thioester intermediate and transferring SUMO-1, -2, or -3 to consensus ψKXE motifs in substrates using only E1, Ubc9, mature SUMO, and ATP [#0, #5]. Ubc9 directly recognizes substrate sumoylation motifs and cooperates with E3 ligases—RanBP2/Nup358, which binds both SUMO and the Ubc9 β-sheet surface to orient the SUMO~E2 thioester for paralog-selective conjugation, and the yeast Siz/Pli/Mms21 ligases [#3, #4, #6, #10]. A noncovalent \\\"backside\\\" interaction between Ubc9 and SUMO, structurally analogous to the Mms2–Ubc13 ubiquitin chain-forming mechanism, is dispensable for mono-SUMOylation but required for poly-SUMO chain assembly; engineered backside-binding inhibitors block heat-shock poly-SUMOylation and arsenic-induced PML degradation without affecting mono-SUMOylation [#7, #8, #15]. Ubc9 activity and substrate selectivity are tuned by modifications of the enzyme itself: autosumoylation at Lys14 redirects target discrimination, Lys65 acetylation (reversed by SIRT1 under hypoxia) selectively dampens conjugation of NDSM substrates, CDK1-dependent Ser71 phosphorylation and subsequent Pin1 isomerization enhance thioester formation, and yeast sumoylation at Lys153 converts Ubc9 into a chain-promoting cofactor [#9, #12, #13, #16]. Beyond catalysis, Ubc9 acts as a SUMO-conjugation-independent coregulator and protein-stability factor—stimulating androgen-receptor and oocyte transcription, and stabilizing GLUT4, XBP1(S), and other clients via catalytically inactive (C93S/C93A) mutants that retain function [#20, #27, #28, #30]. Functionally, Ubc9 is essential for cell viability, cytokinesis and G2/M progression, replication-fork repair, and chromosome segregation [#24, #25, #26, #39], and in vivo it maintains intestinal stem cells, oocyte and beta-cell development, cardiomyocyte protein quality control, and macrophage polarization through sumoylation of substrates including keratin 8, NRF2, lamin A/C, STAT4, and IRF4 [#32, #33, #34, #35, #40, #46, #47].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 1996,\n      \"claim\": \"Established the first physical and genetic links of human UBE2I to recombination/meiosis machinery and demonstrated functional conservation with yeast Ubc9, framing it as a cell-cycle-relevant factor before its enzymatic identity was known.\",\n      \"evidence\": \"Yeast two-hybrid against Rad51/Rad52/p53/UBL1, spermatocyte immunolocalization, and yeast ts-mutant complementation\",\n      \"pmids\": [\"8610150\", \"8921390\", \"8668529\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Yeast two-hybrid interactions lacked biochemical validation\", \"Did not define a molecular activity for the protein\", \"Meiotic role inferred from localization only\"]\n    },\n    {\n      \"year\": 1998,\n      \"claim\": \"Resolved what UBE2I actually does enzymatically: it is the SUMO E2, forming a thioester with SUMO/SMT3 and being required for SUMO conjugation in vivo, defining the entire pathway's E2 step.\",\n      \"evidence\": \"In vitro thioester formation assay plus in vivo complementation in a yeast ubc9 mutant\",\n      \"pmids\": [\"9435231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve substrate-selection rules\", \"E3 ligase requirements not yet defined\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed Ubc9 with E1 can build polymeric SUMO-2/-3 chains and that SUMO-1 cannot self-polymerize, distinguishing mono- from poly-SUMOylation as separable outputs.\",\n      \"evidence\": \"In vitro reconstitution of SUMO chain formation with in vivo immunoblot detection\",\n      \"pmids\": [\"11451954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Surface of Ubc9 mediating chain extension not yet mapped\", \"Physiological triggers of chain formation undefined\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Mapped distinct Ubc9 surfaces for SUMO transfer steps, separating an N-terminal noncovalent SUMO-binding region required for E1-to-E2 transfer from substrate recognition and E2-to-target transfer.\",\n      \"evidence\": \"Site-directed mutagenesis, ITC, NMR chemical shift perturbation, and in vitro conjugation\",\n      \"pmids\": [\"12924945\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"E3-binding surface not yet defined\", \"In vivo consequence of these surface mutations untested\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Defined how an E3 (RanBP2/Nup358) engages Ubc9 via its β-sheet surface to confer paralog-selective conjugation, showing SUMO E2–E3 logic differs from ubiquitin.\",\n      \"evidence\": \"NMR chemical shift perturbation, mutagenesis, and in vitro conjugation of Sp100/PML\",\n      \"pmids\": [\"15608651\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of thioester positioning not yet structurally resolved\", \"Generality across other E3s unknown\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Provided the structural mechanism of SUMO E3 catalysis: a Ubc9–RanBP2–SUMO~RanGAP1 complex showed the E3 binds both SUMO and Ubc9 to optimally orient the thioester, and parallel work reconstituted the minimal active E2.\",\n      \"evidence\": \"X-ray crystallography at 3.0 Å with kinetics; detailed in vitro single/multiple-turnover reconstitution\",\n      \"pmids\": [\"15931224\", \"16275321\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic chemistry of lysine attack not fully resolved\", \"How modifications of Ubc9 alter this geometry untested here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified the noncovalent 'backside' Ubc9–SUMO interface as the determinant of poly-SUMO chain elongation, distinct from mono-SUMOylation and analogous to ubiquitin Mms2–Ubc13 chemistry.\",\n      \"evidence\": \"Crystal structures of noncovalent Ubc9–SUMO1, chain-formation assays, MS linkage analysis\",\n      \"pmids\": [\"17466333\", \"17491593\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo importance of backside binding not yet probed\", \"Substrate determinants directing chain vs. mono unclear\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed autosumoylation at Lys14 is a self-encoded switch that retunes Ubc9 substrate discrimination, creating a SIM-dependent interface that favors some substrates over others.\",\n      \"evidence\": \"Crystal structure of sumoylated Ubc9, conjugation assays with multiple substrates, SIM mutagenesis\",\n      \"pmids\": [\"18691969\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cellular regulation of Ubc9 autosumoylation undefined\", \"Breadth of SIM-dependent substrates not catalogued\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated that Ubc9 uses analogous noncovalent surfaces to engage SUMO and a SUMO-like domain (Rad60 SLD2), partitioning its activities between Nse2-dependent DNA repair and Pli1-dependent global sumoylation/chain formation.\",\n      \"evidence\": \"Crystallography, mutagenesis, and yeast genetic epistasis with in vivo sumoylation assays\",\n      \"pmids\": [\"21444718\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mammalian counterpart of SLD2 partitioning unconfirmed\", \"How surfaces are selected in vivo unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed multiple covalent modifications of Ubc9 (Lys65 acetylation reversed by SIRT1; Lys153 sumoylation in yeast) that switch substrate selectivity and convert Ubc9 between active enzyme and chain-promoting cofactor, linking sumoylation to hypoxia and meiosis.\",\n      \"evidence\": \"In vitro conjugation/chain assays, MS site mapping, mutagenesis, SIRT1 knockdown, yeast meiotic genetics\",\n      \"pmids\": [\"23395904\", \"23644018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Enzymes installing Lys153 sumoylation in vivo not fully defined\", \"Crosstalk among the various Ubc9 modifications unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Engineered backside-binding inhibitors (SUBINs) provided a tool that selectively blocks poly-SUMO chains in cells, confirming the two activities are pharmacologically separable and required for stress-induced PML degradation.\",\n      \"evidence\": \"Phage-display protein engineering, in vitro chain assays, cellular heat-shock and arsenic treatment\",\n      \"pmids\": [\"28784659\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Endogenous regulators that gate backside binding unknown\", \"Range of chain-dependent processes in cells not mapped\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Extended kinase control of Ubc9 by showing Akt phosphorylates Thr35 to boost thioester formation and global SUMOylation, integrating sumoylation with growth-factor signaling.\",\n      \"evidence\": \"In vitro kinase and thioester assays, T35A mutagenesis, co-IP, reporter assays\",\n      \"pmids\": [\"25867063\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab with pleiotropic claims spanning STAT1/CREB and SUMO1 stabilization\", \"In vivo significance of Thr35 phosphorylation untested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected CDK1 phosphorylation of Ubc9 to Pin1 prolyl isomerization as a sequential activation module driving hypersumoylation in glioma stem cells.\",\n      \"evidence\": \"Co-IP, in vitro thioester assays, phosphosite mutagenesis, inhibitor studies, in vivo tumor model\",\n      \"pmids\": [\"38167292\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab; generality beyond glioma stem cells unknown\", \"Direct structural effect of isomerization on the active site not resolved\"]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Established Ubc9 as essential in vertebrate cells with a cytokinesis defect distinct from the yeast G2/M block, showing SUMO conjugation has organism-specific essential roles.\",\n      \"evidence\": \"Tetracycline-repressible conditional knockout in DT40 cells with FACS and nuclear morphology analysis\",\n      \"pmids\": [\"12413887\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Critical SUMO substrates for cytokinesis not identified\", \"Single cell-type system\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Placed Ubc9/SUMO in a defined replication-repair pathway, acting with Mms21 and Sgs1 to resolve damaged-fork cruciforms separately from the Siz1/PCNA/Srs2 route, and in vertebrate G2/M control.\",\n      \"evidence\": \"Yeast genetics with 2D-gel cruciform readout and epistasis; zebrafish dominant-negative/morpholino with cell-cycle FACS\",\n      \"pmids\": [\"17081974\", \"17035631\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Direct SUMO substrates at the fork not pinpointed\", \"Mechanistic basis of zebrafish G2/M arrest unresolved\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Uncovered a SUMO-conjugation-independent coregulatory function: a catalytic-dead Ubc9 still potentiates androgen-receptor transactivation, separating enzymatic from scaffolding roles.\",\n      \"evidence\": \"Yeast two-hybrid, co-IP, reporter assays with C93S mutant\",\n      \"pmids\": [\"10383460\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of conjugation-independent coactivation unknown\", \"Breadth across nuclear receptors not tested here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Generalized the conjugation-independent role to membrane-protein trafficking, with catalytically inactive Ubc9 (C93A) regulating GLUT4 stability and storage-compartment targeting.\",\n      \"evidence\": \"Adenoviral overexpression/siRNA in adipocytes, glucose transport, fractionation, C93A mutant\",\n      \"pmids\": [\"17536066\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Partner proteins mediating GLUT4 effect undefined\", \"Whether SUMO of a third party is required not excluded\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Demonstrated an essential in vivo tissue-maintenance role: inducible intestinal knockout depletes stem cells and disrupts epithelial polarity, with keratin 8 identified as a SUMO target.\",\n      \"evidence\": \"Inducible conditional knockout mouse, histology/IF, in vitro keratin-8 sumoylation\",\n      \"pmids\": [\"20951138\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Causal substrate(s) for stem-cell loss not established\", \"Link between keratin-8 sumoylation and phenotype indirect\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Defined specific substrate-level mechanisms in vivo across tissues—lamin A/C for nucleophagy, STAT4 and IRF4 for macrophage polarization, NRF2 for beta-cell ROS defense, plus oocyte fertility—anchoring Ubc9's physiology to named substrates.\",\n      \"evidence\": \"Cell-type-specific knockouts, SUMO-site mutagenesis (e.g., STAT4 K350R), co-IP, fractionation, in vivo disease/tumor models\",\n      \"pmids\": [\"30744690\", \"36626227\", \"31767832\", \"29299635\", \"31704792\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Each substrate axis is single-lab\", \"Whether SUMOylation is sufficient versus necessary not fully isolated for all targets\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed therapeutically tractable substrate engagement: Ubc9 binds CRMP2 at low-micromolar affinity, and peptide disruption reduces NaV1.7 trafficking and reverses neuropathic pain, illustrating substrate-targeted modulation of Ubc9.\",\n      \"evidence\": \"Microscale thermophoresis, AlphaLISA, peptide inhibitor, patch clamp, in vivo nerve-injury model\",\n      \"pmids\": [\"29847471\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Selectivity of the peptide for the Ubc9–CRMP2 interface incompletely defined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated Ubc9 active-site plasticity by engineering a chimeric E1 that loads native ubiquitin onto Ubc9, enabling tag-directed ubiquitylation, showing the catalytic cleft can accommodate ubiquitin.\",\n      \"evidence\": \"Directed evolution of chimeric E1, in vitro ubiquitylation, E. coli reconstitution\",\n      \"pmids\": [\"35237717\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Native cellular relevance of ubiquitin loading unknown\", \"Engineered system only\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the diverse Ubc9 inputs—covalent modifications, backside/SLD surfaces, E3 partners, and conjugation-independent scaffolding—are integrated to select among hundreds of substrates in a given cell state remains unresolved.\",\n      \"evidence\": \"No single study in the corpus reconciles the regulatory layers into a predictive substrate-selection model\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model linking Ubc9 PTMs to substrate choice in vivo\", \"Conjugation-independent functions lack defined structural mechanism\", \"Relative in vivo contribution of mono- vs poly-SUMOylation per process unmapped\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [0, 3, 4, 5, 8, 34]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [0, 5, 13, 45]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [0, 5]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [20, 27, 28, 30]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [4, 7, 13]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [21, 28, 33, 52]},\n      {\"term_id\": \"GO:0005654\", \"supporting_discovery_ids\": [28]},\n      {\"term_id\": \"GO:0005829\", \"supporting_discovery_ids\": [21]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [0, 1, 5]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [24, 26, 39]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [25, 33]},\n      {\"term_id\": \"R-HSA-9612973\", \"supporting_discovery_ids\": [32, 33, 49]},\n      {\"term_id\": \"R-HSA-168256\", \"supporting_discovery_ids\": [34, 35]}\n    ],\n    \"complexes\": [\n      \"SAE1/SAE2–Ubc9 SUMO E1–E2 system\",\n      \"Ubc9–RanBP2/Nup358–SUMO1–RanGAP1 E3 complex\"\n    ],\n    \"partners\": [\n      \"SUMO1\",\n      \"RanBP2\",\n      \"SAE2\",\n      \"RAD51\",\n      \"RAD52\",\n      \"PIAS/Siz/Mms21 (Nse2)\",\n      \"MEL-18\",\n      \"CRMP2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}