{"gene":"UBE2B","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2000,"finding":"Human RAD18 protein physically interacts with HHR6A (UBE2A) and HHR6B (UBE2B), forming stable protein complexes when co-expressed in yeast cells, purified to near homogeneity; this interaction is proposed to be critical for lesion bypass mechanisms.","method":"Co-expression in yeast, protein complex purification to near homogeneity","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal complex purification, single lab, orthogonal purification and co-expression methods","pmids":["10908344"],"is_preprint":false},{"year":2008,"finding":"Human RAD18 complexed with RAD6B (UBE2B) preferentially binds forked and single-stranded DNA structures at stalled replication forks; the SAP domain of RAD18 (residues 248–282) is essential for this DNA binding and for PCNA monoubiquitination and recruitment of DNA polymerase eta to damage sites.","method":"DNA binding assays with purified protein complexes, SAP domain mutagenesis, in vivo localization, UV sensitivity rescue assays","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro DNA binding assay with defined domain mutants, in vivo localization, functional rescue, multiple orthogonal methods in one study","pmids":["18363965"],"is_preprint":false},{"year":1999,"finding":"RAD6B (HHR6B/UBE2B) mediates ubiquitin-dependent proteolysis of the cAMP transcriptional repressors hICERIIγ and hATF5 in mammalian cells, requiring an active ubiquitin-conjugating enzyme; loss of murine Rad6B (mHR6B−/−) or dominant-negative Cdc34 elevates endogenous ICER protein levels, linking RAD6B to regulation of cAMP-induced transcription.","method":"Yeast-based genetic interaction screen, transfection assays in mammalian cells, analysis of Rad6B-null (mHR6B−/−) mice","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — null mouse model, mammalian transfection assays with dominant-negative/antisense constructs, single lab with multiple approaches","pmids":["10373550"],"is_preprint":false},{"year":2004,"finding":"RAD6B (UBE2B) protein expression is cell cycle regulated with maximal levels in late S/G2 phases; upon DNA damage (adriamycin, cisplatin), RAD6B redistributes from nucleoplasm to chromatin along with RAD18, PCNA, phosphohistone H3, and p53; RAD6B overexpression confers chemoresistance and enhanced post-replication repair (PRR) capacity, while antisense depletion causes chemosensitivity and loss of PRR.","method":"Cell cycle synchronization, in vivo chromatin crosslinking/fractionation, stable overexpression and antisense knockdown, PRR assay, drug sensitivity assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (fractionation, PRR assay, OE/KD), single lab","pmids":["14981545"],"is_preprint":false},{"year":2006,"finding":"The human RAD6B (UBE2B) gene is a direct transcriptional target of TCF-4/β-catenin/p300; Rad6B promoter activity is repressed in normal MCF10A cells due to absence of transcriptionally active β-catenin on TCF binding sequences, and is constitutively active in metastatic MDA-MB-231 cells. Coexpression of β-catenin and p300 derepresses Rad6B promoter in MCF10A cells.","method":"EMSA, Western blot of EMSA, UV cross-linking, chromatin immunoprecipitation assay, luciferase reporter assay","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP, EMSA, reporter assays, multiple orthogonal methods, single lab","pmids":["17050667"],"is_preprint":false},{"year":2008,"finding":"Rad6B (UBE2B) overexpression in MCF10A breast cells induces β-catenin accumulation and stabilization via K63-linked polyubiquitination that renders β-catenin insensitive to 26S proteasome degradation; Rad6B silencing suppresses β-catenin mono- and polyubiquitination and transcriptional activity; in vitro ubiquitination assays confirm Rad6B directly mediates β-catenin polyubiquitination.","method":"Rad6B overexpression/siRNA knockdown in multiple cell lines, in vitro ubiquitination assay, cycloheximide chase, proteasome inhibitor treatment, TOP/Flash reporter assay, chromatin immunoprecipitation","journal":"Cancer research","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — in vitro ubiquitination assay, cycloheximide chase, proteasome inhibitor, multiple cell lines, multiple orthogonal methods","pmids":["18339854"],"is_preprint":false},{"year":2012,"finding":"Rad6B (UBE2B) directly ubiquitinates β-catenin at lysine 394 (within Armadillo repeats 5–7); amino acids 131–181 of β-catenin and amino acids 50–116 of Rad6B are required for their interaction; K394R mutation in β-catenin abrogates ~50% of Rad6B-induced ubiquitination and significantly reduces β-catenin transcriptional activity and steady-state levels.","method":"GST pulldown with deletion mutants, co-immunoprecipitation, in vitro and in vivo ubiquitination assays, site-directed mutagenesis (Lys→Arg), TOP/Flash reporter assay","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstitution with purified proteins, mutagenesis mapping of interaction and ubiquitination site, in vivo and in vitro assays in one rigorous study","pmids":["22705350"],"is_preprint":false},{"year":2013,"finding":"Ube2b (UBE2B) is a direct transcriptional target of androgen receptor (AR) in Sertoli cells; ligand-bound AR directly binds the androgen-responsive element in the Ube2b promoter, upregulates UBE2B expression, and promotes H2A ubiquitylation; UBE2B knockdown blocks testosterone-induced H2A ubiquitylation.","method":"Luciferase reporter assay, EMSA, ChIP, qRT-PCR, Western blot, immunohistochemistry in Sertoli cell-specific AR knockout (S-AR−/y) mice","journal":"Biology of reproduction","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP, EMSA, reporter assay, KO mouse, siRNA knockdown, single lab multiple orthogonal methods","pmids":["23863405"],"is_preprint":false},{"year":2015,"finding":"UBE2B is the predominant E2 enzyme involved in myofibrillar protein loss under catabolic conditions in C2C12 myotubes; UBE2B knockdown decreases total ubiquitin conjugates by 18% and K48-linked ubiquitin conjugates (proteasome substrates) by 28% under dexamethasone-induced catabolism, indicating a direct role in ubiquitin-proteasome-dependent muscle protein breakdown.","method":"E2 expression screen, siRNA knockdown in C2C12 myotubes, quantification of polyUb conjugates and K48-linked ubiquitin conjugates by Western blot","journal":"Journal of cachexia, sarcopenia and muscle","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — siRNA knockdown with specific biochemical readout (K48-Ub conjugates), single lab, single method with quantitative outcome","pmids":["27239408"],"is_preprint":false},{"year":2018,"finding":"RAD6B (UBE2B) polyubiquitinates histones H2A and H2B; loss of RAD6B in male mice results in absence of histone polyubiquitination and male sterility; RNF8 (an E3 ligase) monoubiquitinates H2A and H2B. Senescence also contributes to RAD6B-null male sterility.","method":"RAD6B and RNF8 knockout mouse models, histone ubiquitination assays, offspring counting for fertility assessment","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — KO mouse with specific histone ubiquitination biochemical readout, single lab","pmids":["28825854"],"is_preprint":false},{"year":2019,"finding":"RAD6B (UBE2B) is a principal mediator of translesion synthesis (TLS): a RAD6-selective inhibitor (SMI#9) attenuates cisplatin-induced PCNA monoubiquitination, FANCD2 activation (Fanconi anemia pathway marker), TLS polymerase POL η recruitment, and restart of cisplatin-stalled replication forks; RAD6B silencing or SMI#9 also impairs homologous recombination independently of BRCA1 status; RAD6B modulates cisplatin-induced γH2AX via H2AX monoubiquitination.","method":"RAD6-selective small-molecule inhibitor (SMI#9), RAD6B siRNA knockdown, PCNA ubiquitination assays, DNA fiber assay, DR-GFP-based HR assay, foci formation assays, in vivo xenograft","journal":"Biochimica et biophysica acta. Molecular basis of disease","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal methods (biochemical, genetic, DNA fiber, DR-GFP, in vivo) in single study with clear mechanistic endpoints","pmids":["31639439"],"is_preprint":false},{"year":2019,"finding":"Ube2b (UBE2B) mediates ubiquitination and degradation of DNMT3a in rat dorsal hippocampus following heroin self-administration; Ube2b-dependent DNMT3a degradation leads to demethylation of the CaMKK1 gene promoter, upregulating CaMKK1 and activating CaMKIα/βPIX/Rac1 signaling, which drives actin cytoskeleton remodeling and behavioral plasticity.","method":"In vivo model (heroin self-administration in rats), ubiquitination assays, co-immunoprecipitation, promoter methylation analysis, protein expression assays (Western blot), behavioral experiments","journal":"Molecular psychiatry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vivo model with mechanistic pathway resolution, co-IP, ubiquitination assay, single lab","pmids":["31576007"],"is_preprint":false},{"year":2022,"finding":"UBE2B forms a heterodimeric complex with E3 ligase RAD18 and together monoubiquitinates ZMYM2 at the expense of its polyubiquitination, thereby stabilizing ZMYM2 protein; RAD18 knockdown impairs UBE2B-induced ZMYM2 monoubiquitination and destabilizes ZMYM2; UBE2B overexpression promotes ovarian cancer xenograft growth in a ZMYM2-dependent manner.","method":"Co-immunoprecipitation, immunofluorescence co-localization, cycloheximide chase assay, siRNA knockdown, ubiquitination assay, xenograft tumor model","journal":"Bioengineered","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP, ubiquitination assay, cycloheximide chase, in vivo xenograft, single lab","pmids":["35313791"],"is_preprint":false},{"year":2024,"finding":"UBR4 contains a catalytic module comprising a 'hemiRING' zinc finger, a helical-rich UZI subdomain, and an N-terminal affinity region; the crystal/cryo-EM structure of the UBR4 E2–E3 complex reveals atomic-level specificity determinants of the hemiRING toward cognate E2s UBE2A and UBE2B (UBE2B is a bona fide E2 partner of UBR4); the UZI subdomain allosterically modestly activates the Ub-loaded UBE2A/UBE2B∼Ub, and the intrinsically high lysine reactivity of these E2s cooperates with this activation for substrate specificity.","method":"Structure determination (E2–E3 complex), in vitro ubiquitination assays, mutagenesis, biochemical characterization","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — structural determination of E2–E3 complex with mutagenesis and in vitro ubiquitination assays in one rigorous study","pmids":["38182926"],"is_preprint":false},{"year":2019,"finding":"RAD6B splice variants RAD6BΔexon4 and RAD6Bintron5ins, expressed selectively in melanoma but not normal melanocytes, are translated as 14 and 15 kDa proteins, respectively, and retain functional in vivo ubiquitin-conjugating activity despite their truncated nature.","method":"RT-PCR splice variant characterization, Western blot, in vivo ubiquitin conjugating activity assay, whole exome sequencing of patient melanomas","journal":"Cells","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional ubiquitin conjugating activity confirmed in vivo, protein expression validated, single lab","pmids":["31683936"],"is_preprint":false},{"year":2026,"finding":"UBE2B interacts with E3 ligase BIRC2 to catalyze K63-linked ubiquitination of TRAF1, thereby amplifying NF-κB signaling in gastric cancer; NF-κB subunit P65 directly binds the UBE2B promoter creating a feedforward loop; this UBE2B-BIRC2-TRAF1-P65 axis is a self-sustaining mechanism driving NF-κB hyperactivation and tumor proliferation.","method":"Co-immunoprecipitation, K63-ubiquitination assay, chromatin immunoprecipitation assay, luciferase reporter assay, in vitro and in vivo proliferation assays","journal":"Molecular cancer research : MCR","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — co-IP, K63-ubiquitination assay, ChIP and luciferase reporter, single lab","pmids":["41661096"],"is_preprint":false},{"year":2025,"finding":"UBE2B promotes ubiquitination and degradation of U2AF1 (U2 small nuclear RNA auxiliary factor 1) in endothelial cells during renal ischemia-reperfusion injury, leading to activation of the p53/p21 signaling pathway, endothelial apoptosis, and inhibited proliferation.","method":"UBE2B overexpression/knockdown in endothelial cell models, ubiquitination assay, co-immunoprecipitation, Western blot for p53/p21 pathway","journal":"Molecular biology reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, single paper, limited methodological detail in abstract for ubiquitination mechanism","pmids":["41186784"],"is_preprint":false}],"current_model":"UBE2B (RAD6B/HHR6B) is an E2 ubiquitin-conjugating enzyme that: (1) forms a complex with RAD18, which recognizes stalled replication forks via forked/ssDNA binding to initiate post-replication repair/translesion synthesis, including PCNA monoubiquitination and TLS polymerase recruitment; (2) mediates proteasome-insensitive K63-linked polyubiquitination of β-catenin at K394, stabilizing it and creating a positive feedback loop with Wnt/TCF transcription; (3) ubiquitinates histones H2A and H2B (including monoubiquitination essential for spermatogenesis); (4) targets transcriptional repressors (hICERIIγ, hATF5, DNMT3a) for ubiquitin-mediated degradation; (5) is recruited by the UBR4 E3 ligase through a hemiRING–UZI module for N-degron pathway substrates; and (6) partners with BIRC2 to K63-ubiquitinate TRAF1, amplifying NF-κB signaling."},"narrative":{"mechanistic_narrative":"UBE2B (RAD6B/HHR6B) is an E2 ubiquitin-conjugating enzyme that operates across genome maintenance, transcriptional regulation, and signal amplification by partnering with distinct E3 ligases to determine substrate and ubiquitin-chain identity [PMID:10908344, PMID:18339854, PMID:38182926]. In post-replication repair, UBE2B forms a stable heterodimer with the E3 ligase RAD18 that preferentially binds forked and single-stranded DNA at stalled replication forks through the RAD18 SAP domain, driving PCNA monoubiquitination and recruitment of translesion polymerase POL η [PMID:10908344, PMID:18363965]; UBE2B redistributes from nucleoplasm to chromatin upon DNA damage in late S/G2 and is the principal mediator of translesion synthesis, with its activity also feeding into FANCD2 activation, homologous recombination, and H2AX monoubiquitination [PMID:14981545, PMID:31639439]. Through its catalytic activity UBE2B builds K63-linked polyubiquitin on β-catenin at K394, generating a proteasome-insensitive stabilized pool that drives TCF/β-catenin transcription, while β-catenin reciprocally activates the UBE2B promoter to form a positive feedback loop [PMID:17050667, PMID:18339854, PMID:22705350]. UBE2B further mono- and polyubiquitinates histones H2A and H2B, a chromatin modification induced downstream of androgen receptor signaling in Sertoli cells and essential for spermatogenesis, as RAD6B-null male mice lack histone polyubiquitination and are sterile [PMID:23863405, PMID:28825854]. The enzyme also targets specific proteins for degradative ubiquitination, including the cAMP repressors hICERIIγ and hATF5 and the DNA methyltransferase DNMT3a [PMID:10373550, PMID:31576007], and is recruited as a bona fide E2 partner by the UBR4 N-degron E3 ligase via a hemiRING–UZI catalytic module that allosterically activates the Ub-loaded UBE2B [PMID:38182926]. Additional E3 partnerships extend its reach to oncogenic signaling, where UBE2B cooperates with BIRC2 to K63-ubiquitinate TRAF1 and amplify NF-κB [PMID:41661096] and with RAD18 to monoubiquitinate and stabilize ZMYM2 [PMID:35313791].","teleology":[{"year":1999,"claim":"Established UBE2B as a functional ubiquitin-conjugating enzyme in mammals by linking it to turnover of specific transcriptional repressors, moving it beyond a presumed DNA-repair-only role.","evidence":"Yeast genetic interaction screen, mammalian transfection assays, and Rad6B-null (mHR6B-/-) mice showing elevated ICER levels","pmids":["10373550"],"confidence":"Medium","gaps":["Direct E3 ligase partner for hICERIIγ/hATF5 turnover not identified","Chain type on these substrates not defined"]},{"year":2000,"claim":"Identified the physical RAD18–UBE2B complex, defining the E2–E3 pairing that underlies lesion bypass.","evidence":"Co-expression in yeast with protein complex purification to near homogeneity","pmids":["10908344"],"confidence":"Medium","gaps":["Substrate of the complex not yet shown in this study","Structural basis of the interaction unresolved at this point"]},{"year":2004,"claim":"Showed UBE2B is cell-cycle-regulated and recruited to chromatin upon DNA damage, connecting its abundance and localization to post-replication repair capacity and chemoresistance.","evidence":"Cell cycle synchronization, chromatin fractionation, overexpression/antisense knockdown, PRR and drug-sensitivity assays","pmids":["14981545"],"confidence":"Medium","gaps":["Mechanism of damage-induced chromatin recruitment not defined","Direct ubiquitination targets on chromatin not enumerated here"]},{"year":2008,"claim":"Defined the mechanism of the RAD18–UBE2B complex at stalled forks by showing the RAD18 SAP domain mediates forked/ssDNA binding required for PCNA monoubiquitination and POL η recruitment.","evidence":"DNA-binding assays with purified complexes, SAP-domain mutagenesis, in vivo localization, UV-sensitivity rescue","pmids":["18363965"],"confidence":"High","gaps":["Whether UBE2A vs UBE2B contributions differ at forks not separated","Kinetics of the conjugation reaction not measured"]},{"year":2008,"claim":"Revealed a non-degradative function: UBE2B builds K63-linked, proteasome-insensitive polyubiquitin on β-catenin to stabilize it and promote TCF transcription, establishing a Wnt-pathway role.","evidence":"Overexpression/siRNA in multiple cell lines, in vitro ubiquitination, cycloheximide chase, proteasome inhibition, TOP/Flash reporter","pmids":["18339854"],"confidence":"High","gaps":["Cognate E3 ligase for β-catenin K63-ubiquitination not identified","Deubiquitinase counteracting this modification unknown"]},{"year":2006,"claim":"Closed a regulatory loop by showing UBE2B is itself a direct TCF-4/β-catenin/p300 transcriptional target, rationalizing constitutive UBE2B activity in metastatic cells.","evidence":"EMSA, ChIP, UV cross-linking, luciferase reporter assays in MCF10A vs MDA-MB-231 cells","pmids":["17050667"],"confidence":"Medium","gaps":["In vivo relevance of the feedback loop to tumor progression not tested here","Other transcriptional inputs to the UBE2B promoter not mapped"]},{"year":2012,"claim":"Mapped the β-catenin interaction interface and the ubiquitination acceptor site (K394), providing residue-level mechanism for UBE2B-driven β-catenin stabilization.","evidence":"GST pulldown with deletion mutants, co-IP, in vitro/in vivo ubiquitination, K394R mutagenesis, TOP/Flash reporter","pmids":["22705350"],"confidence":"High","gaps":["~50% of ubiquitination persists in K394R, implying additional acceptor sites unmapped","Structural model of the UBE2B–β-catenin contact absent"]},{"year":2013,"claim":"Placed UBE2B downstream of androgen receptor signaling in Sertoli cells, linking hormonal control to histone H2A ubiquitylation in the male germline.","evidence":"Luciferase reporter, EMSA, ChIP, qRT-PCR, and IHC in Sertoli-cell-specific AR knockout mice","pmids":["23863405"],"confidence":"Medium","gaps":["E3 ligase pairing for AR-induced H2A ubiquitylation not specified","Chain linkage on H2A not defined"]},{"year":2017,"claim":"Demonstrated that UBE2B-dependent histone H2A/H2B polyubiquitination is essential for spermatogenesis, with RAD6B loss causing male sterility.","evidence":"RAD6B and RNF8 knockout mouse models, histone ubiquitination assays, fertility assessment","pmids":["28825854"],"confidence":"Medium","gaps":["Division of labor between RAD6B and RNF8 on H2A/H2B not fully resolved","Contribution of senescence vs direct chromatin defect to sterility not separated"]},{"year":2019,"claim":"Confirmed UBE2B as the principal driver of translesion synthesis using a selective inhibitor, extending its role to Fanconi anemia pathway activation and homologous recombination.","evidence":"RAD6-selective inhibitor SMI#9, siRNA, PCNA ubiquitination assays, DNA fiber, DR-GFP HR assay, xenograft","pmids":["31639439"],"confidence":"High","gaps":["Mechanism of HR involvement independent of PCNA ubiquitination unclear","Off-target effects of SMI#9 not fully excluded"]},{"year":2019,"claim":"Showed UBE2B can degrade DNMT3a in vivo, coupling its activity to DNA demethylation and downstream cytoskeletal/behavioral plasticity in a heroin self-administration model.","evidence":"In vivo rat model, ubiquitination assays, co-IP, promoter methylation analysis, behavioral experiments","pmids":["31576007"],"confidence":"Medium","gaps":["E3 ligase for DNMT3a degradation not identified","Chain type and acceptor lysine on DNMT3a undefined"]},{"year":2019,"claim":"Identified melanoma-selective RAD6B splice variants that remain catalytically active, indicating disease-associated isoforms retain conjugating function.","evidence":"RT-PCR splice variant characterization, Western blot, in vivo ubiquitin-conjugating assay, whole exome sequencing of melanomas","pmids":["31683936"],"confidence":"Medium","gaps":["Substrate spectrum of the truncated variants not defined","Functional consequence for melanoma progression not demonstrated"]},{"year":2022,"claim":"Showed the RAD18–UBE2B pair can act non-degradatively to monoubiquitinate and stabilize ZMYM2, supporting ovarian cancer growth.","evidence":"Co-IP, immunofluorescence co-localization, cycloheximide chase, siRNA, ubiquitination assay, xenograft","pmids":["35313791"],"confidence":"Medium","gaps":["Acceptor lysine on ZMYM2 not mapped","Mechanistic switch between mono- and polyubiquitination of ZMYM2 unresolved"]},{"year":2024,"claim":"Provided the structural basis for UBE2B's recruitment to an E3, defining how the UBR4 hemiRING–UZI module selects and allosterically activates UBE2A/UBE2B for N-degron substrates.","evidence":"Structure determination of the UBR4 E2–E3 complex, mutagenesis, in vitro ubiquitination assays","pmids":["38182926"],"confidence":"High","gaps":["N-degron substrates ubiquitinated via this module not enumerated here","Cellular contexts where UBR4–UBE2B operates not established"]},{"year":2026,"claim":"Extended UBE2B's K63-ubiquitination activity to NF-κB signaling, showing a BIRC2–TRAF1–P65 feedforward loop that sustains its own expression in gastric cancer.","evidence":"Co-IP, K63-ubiquitination assay, ChIP, luciferase reporter, in vitro/in vivo proliferation assays","pmids":["41661096"],"confidence":"Medium","gaps":["Acceptor lysine on TRAF1 not mapped","Generality of the loop beyond gastric cancer untested"]},{"year":null,"claim":"How UBE2B is partitioned among its many E3 partners and chain-type outputs (K48 degradative vs K63/monoubiquitin non-degradative) within a single cell remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unifying model for E3 partner selection in vivo","Determinants of K48 vs K63 vs monoubiquitin output not defined","Relative contribution of UBE2A vs UBE2B across pathways unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140096","term_label":"catalytic activity, acting on a protein","supporting_discovery_ids":[5,6,9,13]},{"term_id":"GO:0016874","term_label":"ligase activity","supporting_discovery_ids":[5,13,14]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[3,9]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[1,10]},{"term_id":"R-HSA-392499","term_label":"Metabolism of proteins","supporting_discovery_ids":[2,8,11]},{"term_id":"R-HSA-162582","term_label":"Signal Transduction","supporting_discovery_ids":[5,6,15]},{"term_id":"R-HSA-4839726","term_label":"Chromatin organization","supporting_discovery_ids":[7,9]}],"complexes":["RAD18-UBE2B (RAD6B) complex"],"partners":["RAD18","UBR4","BIRC2","ZMYM2","CTNNB1","TRAF1","DNMT3A"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P63146","full_name":"Ubiquitin-conjugating enzyme E2 B","aliases":["E2 ubiquitin-conjugating enzyme B","RAD6 homolog B","HR6B","hHR6B","Ubiquitin carrier protein B","Ubiquitin-conjugating enzyme E2-17 kDa","Ubiquitin-protein ligase B"],"length_aa":152,"mass_kda":17.3,"function":"E2 ubiquitin-conjugating enzyme that accepts ubiquitin from the ubiquitin-activating enzyme E1 and transfers it to a E3 ubiquitin-protein ligase (PubMed:16337599, PubMed:17108083, PubMed:17130289, PubMed:1717990, PubMed:20061386). In vitro catalyzes 'Lys-11'-, as well as 'Lys-48'- and 'Lys-63'-linked polyubiquitination (PubMed:20061386). Together with the E3 enzyme BRE1 (RNF20 and/or RNF40), plays a role in transcription regulation by catalyzing the monoubiquitination of histone H2B at 'Lys-120' to form H2BK120ub1 (PubMed:16337599). H2BK120ub1 gives a specific tag for epigenetic transcriptional activation, elongation by RNA polymerase II, telomeric silencing, and is also a prerequisite for H3K4me and H3K79me formation (PubMed:16337599). May play a role in DNA repair (PubMed:8062904). Associates to the E3 ligase RAD18 to form the UBE2B-RAD18 ubiquitin ligase complex involved in mono-ubiquitination of DNA-associated PCNA on 'Lys-164' (PubMed:17108083, PubMed:17130289). In association with the E3 enzyme UBR4, is involved in N-end rule-dependent protein degradation (PubMed:38182926). May be involved in neurite outgrowth (By similarity)","subcellular_location":"Cell membrane; Nucleus","url":"https://www.uniprot.org/uniprotkb/P63146/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UBE2B","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UBE2B","total_profiled":1310},"omim":[{"mim_id":"613831","title":"UBIQUITIN PROTEIN LIGASE E3 COMPONENT N-RECOGNIN 3; UBR3","url":"https://www.omim.org/entry/613831"},{"mim_id":"609134","title":"UBIQUITIN-PROTEIN LIGASE E3 COMPONENT N-RECOGNIN 2; UBR2","url":"https://www.omim.org/entry/609134"},{"mim_id":"606398","title":"ACTIVATING TRANSCRIPTION FACTOR 5; ATF5","url":"https://www.omim.org/entry/606398"},{"mim_id":"179095","title":"UBIQUITIN-CONJUGATING ENZYME E2 B; UBE2B","url":"https://www.omim.org/entry/179095"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Plasma membrane","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"},{"location":"Vesicles","reliability":"Additional"},{"location":"Flagellar centriole","reliability":"Additional"},{"location":"Mid piece","reliability":"Additional"},{"location":"Principal piece","reliability":"Additional"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in all","driving_tissues":[{"tissue":"skeletal muscle","ntpm":202.4}],"url":"https://www.proteinatlas.org/search/UBE2B"},"hgnc":{"alias_symbol":["UBC2","HHR6B","RAD6B"],"prev_symbol":[]},"alphafold":{"accession":"P63146","domains":[{"cath_id":"3.10.110.10","chopping":"3-148","consensus_level":"high","plddt":95.995,"start":3,"end":148}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P63146","model_url":"https://alphafold.ebi.ac.uk/files/AF-P63146-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P63146-F1-predicted_aligned_error_v6.png","plddt_mean":95.69},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UBE2B","jax_strain_url":"https://www.jax.org/strain/search?query=UBE2B"},"sequence":{"accession":"P63146","fasta_url":"https://rest.uniprot.org/uniprotkb/P63146.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P63146/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P63146"}},"corpus_meta":[{"pmid":"27235675","id":"PMC_27235675","title":"Up-regulation of miR-455-5p by the TGF-β-SMAD signalling axis promotes the proliferation of oral squamous cancer cells by targeting UBE2B.","date":"2016","source":"The Journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/27235675","citation_count":81,"is_preprint":false},{"pmid":"10373550","id":"PMC_10373550","title":"Human Cdc34 and Rad6B ubiquitin-conjugating enzymes target repressors of cyclic AMP-induced transcription for proteolysis.","date":"1999","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10373550","citation_count":69,"is_preprint":false},{"pmid":"10908344","id":"PMC_10908344","title":"The human RAD18 gene product interacts with HHR6A and HHR6B.","date":"2000","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/10908344","citation_count":61,"is_preprint":false},{"pmid":"18363965","id":"PMC_18363965","title":"Recognition of forked and single-stranded DNA structures by human RAD18 complexed with RAD6B protein triggers its recruitment to stalled replication forks.","date":"2008","source":"Genes to cells : devoted to molecular & cellular mechanisms","url":"https://pubmed.ncbi.nlm.nih.gov/18363965","citation_count":58,"is_preprint":false},{"pmid":"18339854","id":"PMC_18339854","title":"Rad6B is a positive regulator of beta-catenin stabilization.","date":"2008","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/18339854","citation_count":51,"is_preprint":false},{"pmid":"1559696","id":"PMC_1559696","title":"Localization of two human homologs, HHR6A and HHR6B, of the yeast DNA repair gene RAD6 to chromosomes Xq24-q25 and 5q23-q31.","date":"1992","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/1559696","citation_count":49,"is_preprint":false},{"pmid":"14981545","id":"PMC_14981545","title":"RAD6B overexpression confers chemoresistance: RAD6 expression during cell cycle and its redistribution to chromatin during DNA damage-induced response.","date":"2004","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/14981545","citation_count":37,"is_preprint":false},{"pmid":"12784252","id":"PMC_12784252","title":"Spermatid nuclear and sperm periaxonemal anomalies in the mouse Ube2b null mutant.","date":"2003","source":"Molecular reproduction and development","url":"https://pubmed.ncbi.nlm.nih.gov/12784252","citation_count":37,"is_preprint":false},{"pmid":"22705350","id":"PMC_22705350","title":"Lysine 394 is a novel Rad6B-induced ubiquitination site on beta-catenin.","date":"2012","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/22705350","citation_count":26,"is_preprint":false},{"pmid":"28825854","id":"PMC_28825854","title":"Function of RAD6B and RNF8 in spermatogenesis.","date":"2018","source":"Cell cycle (Georgetown, Tex.)","url":"https://pubmed.ncbi.nlm.nih.gov/28825854","citation_count":24,"is_preprint":false},{"pmid":"27239408","id":"PMC_27239408","title":"UBE2B is implicated in myofibrillar protein loss in catabolic C2C12 myotubes.","date":"2015","source":"Journal of cachexia, sarcopenia and muscle","url":"https://pubmed.ncbi.nlm.nih.gov/27239408","citation_count":24,"is_preprint":false},{"pmid":"18497339","id":"PMC_18497339","title":"Novel variants in UBE2B gene and idiopathic male infertility.","date":"2008","source":"Journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/18497339","citation_count":23,"is_preprint":false},{"pmid":"17050667","id":"PMC_17050667","title":"Essential role of T-cell factor/beta-catenin in regulation of Rad6B: a potential mechanism for Rad6B overexpression in breast cancer cells.","date":"2006","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/17050667","citation_count":23,"is_preprint":false},{"pmid":"23863405","id":"PMC_23863405","title":"Identification of Ube2b as a novel target of androgen receptor in mouse sertoli cells.","date":"2013","source":"Biology of reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/23863405","citation_count":22,"is_preprint":false},{"pmid":"31639439","id":"PMC_31639439","title":"RAD6B is a major mediator of triple negative breast cancer cisplatin resistance: Regulation of translesion synthesis/Fanconi anemia crosstalk and BRCA1 independence.","date":"2019","source":"Biochimica et biophysica acta. Molecular basis of disease","url":"https://pubmed.ncbi.nlm.nih.gov/31639439","citation_count":22,"is_preprint":false},{"pmid":"21767405","id":"PMC_21767405","title":"Rad6B acts downstream of Wnt signaling to stabilize β-catenin: Implications for a novel Wnt/β-catenin target.","date":"2011","source":"Journal of molecular signaling","url":"https://pubmed.ncbi.nlm.nih.gov/21767405","citation_count":22,"is_preprint":false},{"pmid":"38182926","id":"PMC_38182926","title":"UBE2A and UBE2B are recruited by an atypical E3 ligase module in UBR4.","date":"2024","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/38182926","citation_count":21,"is_preprint":false},{"pmid":"18385908","id":"PMC_18385908","title":"Novel UBE2B-associated polymorphisms in an azoospermic/oligozoospermic population.","date":"2008","source":"Asian journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/18385908","citation_count":21,"is_preprint":false},{"pmid":"31507381","id":"PMC_31507381","title":"RAD6B Plays a Critical Role in Neuronal DNA Damage Response to Resist Neurodegeneration.","date":"2019","source":"Frontiers in cellular neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/31507381","citation_count":17,"is_preprint":false},{"pmid":"23378580","id":"PMC_23378580","title":"UBE2B mRNA alterations are associated with severe oligozoospermia in infertile men.","date":"2013","source":"Molecular human reproduction","url":"https://pubmed.ncbi.nlm.nih.gov/23378580","citation_count":13,"is_preprint":false},{"pmid":"26223869","id":"PMC_26223869","title":"A functional variant in the UBE2B gene promoter is associated with idiopathic azoospermia.","date":"2015","source":"Reproductive biology and endocrinology : RB&E","url":"https://pubmed.ncbi.nlm.nih.gov/26223869","citation_count":12,"is_preprint":false},{"pmid":"35313791","id":"PMC_35313791","title":"UBE2B promotes ovarian cancer growth via promoting RAD18 mediated ZMYM2 monoubiquitination and stabilization.","date":"2022","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/35313791","citation_count":11,"is_preprint":false},{"pmid":"31576007","id":"PMC_31576007","title":"Ube2b-dependent degradation of DNMT3a relieves a transcriptional brake on opiate-induced synaptic and behavioral plasticity.","date":"2019","source":"Molecular psychiatry","url":"https://pubmed.ncbi.nlm.nih.gov/31576007","citation_count":11,"is_preprint":false},{"pmid":"36828823","id":"PMC_36828823","title":"From tuberculosis bedside to bench: UBE2B splicing as a potential biomarker and its regulatory mechanism.","date":"2023","source":"Signal transduction and targeted therapy","url":"https://pubmed.ncbi.nlm.nih.gov/36828823","citation_count":10,"is_preprint":false},{"pmid":"33181138","id":"PMC_33181138","title":"RAD6B Loss Disrupts Expression of Melanoma Phenotype in Part by Inhibiting WNT/β-Catenin Signaling.","date":"2020","source":"The American journal of pathology","url":"https://pubmed.ncbi.nlm.nih.gov/33181138","citation_count":9,"is_preprint":false},{"pmid":"31683936","id":"PMC_31683936","title":"Alternative Splicing of RAD6B and Not RAD6A is Selectively Increased in Melanoma: Identification and Functional Characterization.","date":"2019","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/31683936","citation_count":7,"is_preprint":false},{"pmid":"19466589","id":"PMC_19466589","title":"Utility of DNA postreplication repair protein Rad6B in neoadjuvant chemotherapy response.","date":"2009","source":"Medical oncology (Northwood, London, England)","url":"https://pubmed.ncbi.nlm.nih.gov/19466589","citation_count":7,"is_preprint":false},{"pmid":"34632937","id":"PMC_34632937","title":"Upregulation of ubiquitin conjugating enzyme E2B (Ube2b) ameliorates neuropathic pain by regulating Kcna2 (potassium voltage-gated channel subfamily A member 2) in primary afferent neurons.","date":"2021","source":"Bioengineered","url":"https://pubmed.ncbi.nlm.nih.gov/34632937","citation_count":7,"is_preprint":false},{"pmid":"23079972","id":"PMC_23079972","title":"Genetic association of UBE2B variants with susceptibility to male infertility in a Northeast Chinese population.","date":"2012","source":"Genetics and molecular research : GMR","url":"https://pubmed.ncbi.nlm.nih.gov/23079972","citation_count":7,"is_preprint":false},{"pmid":"34774969","id":"PMC_34774969","title":"The Role of RAD6B and PEDF in Retinal Degeneration.","date":"2021","source":"Neuroscience","url":"https://pubmed.ncbi.nlm.nih.gov/34774969","citation_count":4,"is_preprint":false},{"pmid":"32868078","id":"PMC_32868078","title":"Loss of RAD6B induces degeneration of the cochlea in mice.","date":"2020","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/32868078","citation_count":4,"is_preprint":false},{"pmid":"24873167","id":"PMC_24873167","title":"[UBE2B gene and male infertility: an update].","date":"2014","source":"Zhonghua nan ke xue = National journal of andrology","url":"https://pubmed.ncbi.nlm.nih.gov/24873167","citation_count":1,"is_preprint":false},{"pmid":"41661096","id":"PMC_41661096","title":"UBE2B Drives NF-κB Signaling and Gastric Cancer Progression through BIRC2-Mediated K63-Linked Ubiquitination of TRAF1.","date":"2026","source":"Molecular cancer research : MCR","url":"https://pubmed.ncbi.nlm.nih.gov/41661096","citation_count":1,"is_preprint":false},{"pmid":"19548583","id":"PMC_19548583","title":"[Effect of hydroquinone on the expression of ubiquitin-conjugating enzyme Rad6B in human L-02 hepatic cells].","date":"2009","source":"Wei sheng yan jiu = Journal of hygiene research","url":"https://pubmed.ncbi.nlm.nih.gov/19548583","citation_count":0,"is_preprint":false},{"pmid":"41186784","id":"PMC_41186784","title":"Targeting UBE2B-mediated U2AF1 degradation to alleviate endothelial dysfunction in renal ischemia-reperfusion injury: therapeutic potential of semaglutide.","date":"2025","source":"Molecular biology reports","url":"https://pubmed.ncbi.nlm.nih.gov/41186784","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":20020,"output_tokens":4868,"usd":0.06654,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":12949,"output_tokens":4853,"usd":0.093035,"stage2_stop_reason":"end_turn"},"total_usd":0.159575,"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\": 2000,\n      \"finding\": \"Human RAD18 protein physically interacts with HHR6A (UBE2A) and HHR6B (UBE2B), forming stable protein complexes when co-expressed in yeast cells, purified to near homogeneity; this interaction is proposed to be critical for lesion bypass mechanisms.\",\n      \"method\": \"Co-expression in yeast, protein complex purification to near homogeneity\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal complex purification, single lab, orthogonal purification and co-expression methods\",\n      \"pmids\": [\"10908344\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Human RAD18 complexed with RAD6B (UBE2B) preferentially binds forked and single-stranded DNA structures at stalled replication forks; the SAP domain of RAD18 (residues 248–282) is essential for this DNA binding and for PCNA monoubiquitination and recruitment of DNA polymerase eta to damage sites.\",\n      \"method\": \"DNA binding assays with purified protein complexes, SAP domain mutagenesis, in vivo localization, UV sensitivity rescue assays\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro DNA binding assay with defined domain mutants, in vivo localization, functional rescue, multiple orthogonal methods in one study\",\n      \"pmids\": [\"18363965\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"RAD6B (HHR6B/UBE2B) mediates ubiquitin-dependent proteolysis of the cAMP transcriptional repressors hICERIIγ and hATF5 in mammalian cells, requiring an active ubiquitin-conjugating enzyme; loss of murine Rad6B (mHR6B−/−) or dominant-negative Cdc34 elevates endogenous ICER protein levels, linking RAD6B to regulation of cAMP-induced transcription.\",\n      \"method\": \"Yeast-based genetic interaction screen, transfection assays in mammalian cells, analysis of Rad6B-null (mHR6B−/−) mice\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — null mouse model, mammalian transfection assays with dominant-negative/antisense constructs, single lab with multiple approaches\",\n      \"pmids\": [\"10373550\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"RAD6B (UBE2B) protein expression is cell cycle regulated with maximal levels in late S/G2 phases; upon DNA damage (adriamycin, cisplatin), RAD6B redistributes from nucleoplasm to chromatin along with RAD18, PCNA, phosphohistone H3, and p53; RAD6B overexpression confers chemoresistance and enhanced post-replication repair (PRR) capacity, while antisense depletion causes chemosensitivity and loss of PRR.\",\n      \"method\": \"Cell cycle synchronization, in vivo chromatin crosslinking/fractionation, stable overexpression and antisense knockdown, PRR assay, drug sensitivity assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (fractionation, PRR assay, OE/KD), single lab\",\n      \"pmids\": [\"14981545\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"The human RAD6B (UBE2B) gene is a direct transcriptional target of TCF-4/β-catenin/p300; Rad6B promoter activity is repressed in normal MCF10A cells due to absence of transcriptionally active β-catenin on TCF binding sequences, and is constitutively active in metastatic MDA-MB-231 cells. Coexpression of β-catenin and p300 derepresses Rad6B promoter in MCF10A cells.\",\n      \"method\": \"EMSA, Western blot of EMSA, UV cross-linking, chromatin immunoprecipitation assay, luciferase reporter assay\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP, EMSA, reporter assays, multiple orthogonal methods, single lab\",\n      \"pmids\": [\"17050667\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Rad6B (UBE2B) overexpression in MCF10A breast cells induces β-catenin accumulation and stabilization via K63-linked polyubiquitination that renders β-catenin insensitive to 26S proteasome degradation; Rad6B silencing suppresses β-catenin mono- and polyubiquitination and transcriptional activity; in vitro ubiquitination assays confirm Rad6B directly mediates β-catenin polyubiquitination.\",\n      \"method\": \"Rad6B overexpression/siRNA knockdown in multiple cell lines, in vitro ubiquitination assay, cycloheximide chase, proteasome inhibitor treatment, TOP/Flash reporter assay, chromatin immunoprecipitation\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — in vitro ubiquitination assay, cycloheximide chase, proteasome inhibitor, multiple cell lines, multiple orthogonal methods\",\n      \"pmids\": [\"18339854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Rad6B (UBE2B) directly ubiquitinates β-catenin at lysine 394 (within Armadillo repeats 5–7); amino acids 131–181 of β-catenin and amino acids 50–116 of Rad6B are required for their interaction; K394R mutation in β-catenin abrogates ~50% of Rad6B-induced ubiquitination and significantly reduces β-catenin transcriptional activity and steady-state levels.\",\n      \"method\": \"GST pulldown with deletion mutants, co-immunoprecipitation, in vitro and in vivo ubiquitination assays, site-directed mutagenesis (Lys→Arg), TOP/Flash reporter assay\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstitution with purified proteins, mutagenesis mapping of interaction and ubiquitination site, in vivo and in vitro assays in one rigorous study\",\n      \"pmids\": [\"22705350\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"Ube2b (UBE2B) is a direct transcriptional target of androgen receptor (AR) in Sertoli cells; ligand-bound AR directly binds the androgen-responsive element in the Ube2b promoter, upregulates UBE2B expression, and promotes H2A ubiquitylation; UBE2B knockdown blocks testosterone-induced H2A ubiquitylation.\",\n      \"method\": \"Luciferase reporter assay, EMSA, ChIP, qRT-PCR, Western blot, immunohistochemistry in Sertoli cell-specific AR knockout (S-AR−/y) mice\",\n      \"journal\": \"Biology of reproduction\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — ChIP, EMSA, reporter assay, KO mouse, siRNA knockdown, single lab multiple orthogonal methods\",\n      \"pmids\": [\"23863405\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"UBE2B is the predominant E2 enzyme involved in myofibrillar protein loss under catabolic conditions in C2C12 myotubes; UBE2B knockdown decreases total ubiquitin conjugates by 18% and K48-linked ubiquitin conjugates (proteasome substrates) by 28% under dexamethasone-induced catabolism, indicating a direct role in ubiquitin-proteasome-dependent muscle protein breakdown.\",\n      \"method\": \"E2 expression screen, siRNA knockdown in C2C12 myotubes, quantification of polyUb conjugates and K48-linked ubiquitin conjugates by Western blot\",\n      \"journal\": \"Journal of cachexia, sarcopenia and muscle\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — siRNA knockdown with specific biochemical readout (K48-Ub conjugates), single lab, single method with quantitative outcome\",\n      \"pmids\": [\"27239408\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"RAD6B (UBE2B) polyubiquitinates histones H2A and H2B; loss of RAD6B in male mice results in absence of histone polyubiquitination and male sterility; RNF8 (an E3 ligase) monoubiquitinates H2A and H2B. Senescence also contributes to RAD6B-null male sterility.\",\n      \"method\": \"RAD6B and RNF8 knockout mouse models, histone ubiquitination assays, offspring counting for fertility assessment\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — KO mouse with specific histone ubiquitination biochemical readout, single lab\",\n      \"pmids\": [\"28825854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAD6B (UBE2B) is a principal mediator of translesion synthesis (TLS): a RAD6-selective inhibitor (SMI#9) attenuates cisplatin-induced PCNA monoubiquitination, FANCD2 activation (Fanconi anemia pathway marker), TLS polymerase POL η recruitment, and restart of cisplatin-stalled replication forks; RAD6B silencing or SMI#9 also impairs homologous recombination independently of BRCA1 status; RAD6B modulates cisplatin-induced γH2AX via H2AX monoubiquitination.\",\n      \"method\": \"RAD6-selective small-molecule inhibitor (SMI#9), RAD6B siRNA knockdown, PCNA ubiquitination assays, DNA fiber assay, DR-GFP-based HR assay, foci formation assays, in vivo xenograft\",\n      \"journal\": \"Biochimica et biophysica acta. Molecular basis of disease\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal methods (biochemical, genetic, DNA fiber, DR-GFP, in vivo) in single study with clear mechanistic endpoints\",\n      \"pmids\": [\"31639439\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Ube2b (UBE2B) mediates ubiquitination and degradation of DNMT3a in rat dorsal hippocampus following heroin self-administration; Ube2b-dependent DNMT3a degradation leads to demethylation of the CaMKK1 gene promoter, upregulating CaMKK1 and activating CaMKIα/βPIX/Rac1 signaling, which drives actin cytoskeleton remodeling and behavioral plasticity.\",\n      \"method\": \"In vivo model (heroin self-administration in rats), ubiquitination assays, co-immunoprecipitation, promoter methylation analysis, protein expression assays (Western blot), behavioral experiments\",\n      \"journal\": \"Molecular psychiatry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vivo model with mechanistic pathway resolution, co-IP, ubiquitination assay, single lab\",\n      \"pmids\": [\"31576007\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"UBE2B forms a heterodimeric complex with E3 ligase RAD18 and together monoubiquitinates ZMYM2 at the expense of its polyubiquitination, thereby stabilizing ZMYM2 protein; RAD18 knockdown impairs UBE2B-induced ZMYM2 monoubiquitination and destabilizes ZMYM2; UBE2B overexpression promotes ovarian cancer xenograft growth in a ZMYM2-dependent manner.\",\n      \"method\": \"Co-immunoprecipitation, immunofluorescence co-localization, cycloheximide chase assay, siRNA knockdown, ubiquitination assay, xenograft tumor model\",\n      \"journal\": \"Bioengineered\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP, ubiquitination assay, cycloheximide chase, in vivo xenograft, single lab\",\n      \"pmids\": [\"35313791\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"UBR4 contains a catalytic module comprising a 'hemiRING' zinc finger, a helical-rich UZI subdomain, and an N-terminal affinity region; the crystal/cryo-EM structure of the UBR4 E2–E3 complex reveals atomic-level specificity determinants of the hemiRING toward cognate E2s UBE2A and UBE2B (UBE2B is a bona fide E2 partner of UBR4); the UZI subdomain allosterically modestly activates the Ub-loaded UBE2A/UBE2B∼Ub, and the intrinsically high lysine reactivity of these E2s cooperates with this activation for substrate specificity.\",\n      \"method\": \"Structure determination (E2–E3 complex), in vitro ubiquitination assays, mutagenesis, biochemical characterization\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structural determination of E2–E3 complex with mutagenesis and in vitro ubiquitination assays in one rigorous study\",\n      \"pmids\": [\"38182926\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAD6B splice variants RAD6BΔexon4 and RAD6Bintron5ins, expressed selectively in melanoma but not normal melanocytes, are translated as 14 and 15 kDa proteins, respectively, and retain functional in vivo ubiquitin-conjugating activity despite their truncated nature.\",\n      \"method\": \"RT-PCR splice variant characterization, Western blot, in vivo ubiquitin conjugating activity assay, whole exome sequencing of patient melanomas\",\n      \"journal\": \"Cells\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional ubiquitin conjugating activity confirmed in vivo, protein expression validated, single lab\",\n      \"pmids\": [\"31683936\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"UBE2B interacts with E3 ligase BIRC2 to catalyze K63-linked ubiquitination of TRAF1, thereby amplifying NF-κB signaling in gastric cancer; NF-κB subunit P65 directly binds the UBE2B promoter creating a feedforward loop; this UBE2B-BIRC2-TRAF1-P65 axis is a self-sustaining mechanism driving NF-κB hyperactivation and tumor proliferation.\",\n      \"method\": \"Co-immunoprecipitation, K63-ubiquitination assay, chromatin immunoprecipitation assay, luciferase reporter assay, in vitro and in vivo proliferation assays\",\n      \"journal\": \"Molecular cancer research : MCR\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — co-IP, K63-ubiquitination assay, ChIP and luciferase reporter, single lab\",\n      \"pmids\": [\"41661096\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"UBE2B promotes ubiquitination and degradation of U2AF1 (U2 small nuclear RNA auxiliary factor 1) in endothelial cells during renal ischemia-reperfusion injury, leading to activation of the p53/p21 signaling pathway, endothelial apoptosis, and inhibited proliferation.\",\n      \"method\": \"UBE2B overexpression/knockdown in endothelial cell models, ubiquitination assay, co-immunoprecipitation, Western blot for p53/p21 pathway\",\n      \"journal\": \"Molecular biology reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, single paper, limited methodological detail in abstract for ubiquitination mechanism\",\n      \"pmids\": [\"41186784\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"UBE2B (RAD6B/HHR6B) is an E2 ubiquitin-conjugating enzyme that: (1) forms a complex with RAD18, which recognizes stalled replication forks via forked/ssDNA binding to initiate post-replication repair/translesion synthesis, including PCNA monoubiquitination and TLS polymerase recruitment; (2) mediates proteasome-insensitive K63-linked polyubiquitination of β-catenin at K394, stabilizing it and creating a positive feedback loop with Wnt/TCF transcription; (3) ubiquitinates histones H2A and H2B (including monoubiquitination essential for spermatogenesis); (4) targets transcriptional repressors (hICERIIγ, hATF5, DNMT3a) for ubiquitin-mediated degradation; (5) is recruited by the UBR4 E3 ligase through a hemiRING–UZI module for N-degron pathway substrates; and (6) partners with BIRC2 to K63-ubiquitinate TRAF1, amplifying NF-κB signaling.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"UBE2B (RAD6B/HHR6B) is an E2 ubiquitin-conjugating enzyme that operates across genome maintenance, transcriptional regulation, and signal amplification by partnering with distinct E3 ligases to determine substrate and ubiquitin-chain identity [#0, #5, #13]. In post-replication repair, UBE2B forms a stable heterodimer with the E3 ligase RAD18 that preferentially binds forked and single-stranded DNA at stalled replication forks through the RAD18 SAP domain, driving PCNA monoubiquitination and recruitment of translesion polymerase POL η [#0, #1]; UBE2B redistributes from nucleoplasm to chromatin upon DNA damage in late S/G2 and is the principal mediator of translesion synthesis, with its activity also feeding into FANCD2 activation, homologous recombination, and H2AX monoubiquitination [#3, #10]. Through its catalytic activity UBE2B builds K63-linked polyubiquitin on β-catenin at K394, generating a proteasome-insensitive stabilized pool that drives TCF/β-catenin transcription, while β-catenin reciprocally activates the UBE2B promoter to form a positive feedback loop [#4, #5, #6]. UBE2B further mono- and polyubiquitinates histones H2A and H2B, a chromatin modification induced downstream of androgen receptor signaling in Sertoli cells and essential for spermatogenesis, as RAD6B-null male mice lack histone polyubiquitination and are sterile [#7, #9]. The enzyme also targets specific proteins for degradative ubiquitination, including the cAMP repressors hICERIIγ and hATF5 and the DNA methyltransferase DNMT3a [#2, #11], and is recruited as a bona fide E2 partner by the UBR4 N-degron E3 ligase via a hemiRING–UZI catalytic module that allosterically activates the Ub-loaded UBE2B [#13]. Additional E3 partnerships extend its reach to oncogenic signaling, where UBE2B cooperates with BIRC2 to K63-ubiquitinate TRAF1 and amplify NF-κB [#15] and with RAD18 to monoubiquitinate and stabilize ZMYM2 [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established UBE2B as a functional ubiquitin-conjugating enzyme in mammals by linking it to turnover of specific transcriptional repressors, moving it beyond a presumed DNA-repair-only role.\",\n      \"evidence\": \"Yeast genetic interaction screen, mammalian transfection assays, and Rad6B-null (mHR6B-/-) mice showing elevated ICER levels\",\n      \"pmids\": [\"10373550\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct E3 ligase partner for hICERIIγ/hATF5 turnover not identified\", \"Chain type on these substrates not defined\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Identified the physical RAD18–UBE2B complex, defining the E2–E3 pairing that underlies lesion bypass.\",\n      \"evidence\": \"Co-expression in yeast with protein complex purification to near homogeneity\",\n      \"pmids\": [\"10908344\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate of the complex not yet shown in this study\", \"Structural basis of the interaction unresolved at this point\"]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Showed UBE2B is cell-cycle-regulated and recruited to chromatin upon DNA damage, connecting its abundance and localization to post-replication repair capacity and chemoresistance.\",\n      \"evidence\": \"Cell cycle synchronization, chromatin fractionation, overexpression/antisense knockdown, PRR and drug-sensitivity assays\",\n      \"pmids\": [\"14981545\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Mechanism of damage-induced chromatin recruitment not defined\", \"Direct ubiquitination targets on chromatin not enumerated here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Defined the mechanism of the RAD18–UBE2B complex at stalled forks by showing the RAD18 SAP domain mediates forked/ssDNA binding required for PCNA monoubiquitination and POL η recruitment.\",\n      \"evidence\": \"DNA-binding assays with purified complexes, SAP-domain mutagenesis, in vivo localization, UV-sensitivity rescue\",\n      \"pmids\": [\"18363965\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether UBE2A vs UBE2B contributions differ at forks not separated\", \"Kinetics of the conjugation reaction not measured\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed a non-degradative function: UBE2B builds K63-linked, proteasome-insensitive polyubiquitin on β-catenin to stabilize it and promote TCF transcription, establishing a Wnt-pathway role.\",\n      \"evidence\": \"Overexpression/siRNA in multiple cell lines, in vitro ubiquitination, cycloheximide chase, proteasome inhibition, TOP/Flash reporter\",\n      \"pmids\": [\"18339854\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Cognate E3 ligase for β-catenin K63-ubiquitination not identified\", \"Deubiquitinase counteracting this modification unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Closed a regulatory loop by showing UBE2B is itself a direct TCF-4/β-catenin/p300 transcriptional target, rationalizing constitutive UBE2B activity in metastatic cells.\",\n      \"evidence\": \"EMSA, ChIP, UV cross-linking, luciferase reporter assays in MCF10A vs MDA-MB-231 cells\",\n      \"pmids\": [\"17050667\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo relevance of the feedback loop to tumor progression not tested here\", \"Other transcriptional inputs to the UBE2B promoter not mapped\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Mapped the β-catenin interaction interface and the ubiquitination acceptor site (K394), providing residue-level mechanism for UBE2B-driven β-catenin stabilization.\",\n      \"evidence\": \"GST pulldown with deletion mutants, co-IP, in vitro/in vivo ubiquitination, K394R mutagenesis, TOP/Flash reporter\",\n      \"pmids\": [\"22705350\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"~50% of ubiquitination persists in K394R, implying additional acceptor sites unmapped\", \"Structural model of the UBE2B–β-catenin contact absent\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Placed UBE2B downstream of androgen receptor signaling in Sertoli cells, linking hormonal control to histone H2A ubiquitylation in the male germline.\",\n      \"evidence\": \"Luciferase reporter, EMSA, ChIP, qRT-PCR, and IHC in Sertoli-cell-specific AR knockout mice\",\n      \"pmids\": [\"23863405\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"E3 ligase pairing for AR-induced H2A ubiquitylation not specified\", \"Chain linkage on H2A not defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Demonstrated that UBE2B-dependent histone H2A/H2B polyubiquitination is essential for spermatogenesis, with RAD6B loss causing male sterility.\",\n      \"evidence\": \"RAD6B and RNF8 knockout mouse models, histone ubiquitination assays, fertility assessment\",\n      \"pmids\": [\"28825854\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Division of labor between RAD6B and RNF8 on H2A/H2B not fully resolved\", \"Contribution of senescence vs direct chromatin defect to sterility not separated\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Confirmed UBE2B as the principal driver of translesion synthesis using a selective inhibitor, extending its role to Fanconi anemia pathway activation and homologous recombination.\",\n      \"evidence\": \"RAD6-selective inhibitor SMI#9, siRNA, PCNA ubiquitination assays, DNA fiber, DR-GFP HR assay, xenograft\",\n      \"pmids\": [\"31639439\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism of HR involvement independent of PCNA ubiquitination unclear\", \"Off-target effects of SMI#9 not fully excluded\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Showed UBE2B can degrade DNMT3a in vivo, coupling its activity to DNA demethylation and downstream cytoskeletal/behavioral plasticity in a heroin self-administration model.\",\n      \"evidence\": \"In vivo rat model, ubiquitination assays, co-IP, promoter methylation analysis, behavioral experiments\",\n      \"pmids\": [\"31576007\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"E3 ligase for DNMT3a degradation not identified\", \"Chain type and acceptor lysine on DNMT3a undefined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified melanoma-selective RAD6B splice variants that remain catalytically active, indicating disease-associated isoforms retain conjugating function.\",\n      \"evidence\": \"RT-PCR splice variant characterization, Western blot, in vivo ubiquitin-conjugating assay, whole exome sequencing of melanomas\",\n      \"pmids\": [\"31683936\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Substrate spectrum of the truncated variants not defined\", \"Functional consequence for melanoma progression not demonstrated\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Showed the RAD18–UBE2B pair can act non-degradatively to monoubiquitinate and stabilize ZMYM2, supporting ovarian cancer growth.\",\n      \"evidence\": \"Co-IP, immunofluorescence co-localization, cycloheximide chase, siRNA, ubiquitination assay, xenograft\",\n      \"pmids\": [\"35313791\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acceptor lysine on ZMYM2 not mapped\", \"Mechanistic switch between mono- and polyubiquitination of ZMYM2 unresolved\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the structural basis for UBE2B's recruitment to an E3, defining how the UBR4 hemiRING–UZI module selects and allosterically activates UBE2A/UBE2B for N-degron substrates.\",\n      \"evidence\": \"Structure determination of the UBR4 E2–E3 complex, mutagenesis, in vitro ubiquitination assays\",\n      \"pmids\": [\"38182926\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"N-degron substrates ubiquitinated via this module not enumerated here\", \"Cellular contexts where UBR4–UBE2B operates not established\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Extended UBE2B's K63-ubiquitination activity to NF-κB signaling, showing a BIRC2–TRAF1–P65 feedforward loop that sustains its own expression in gastric cancer.\",\n      \"evidence\": \"Co-IP, K63-ubiquitination assay, ChIP, luciferase reporter, in vitro/in vivo proliferation assays\",\n      \"pmids\": [\"41661096\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Acceptor lysine on TRAF1 not mapped\", \"Generality of the loop beyond gastric cancer untested\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How UBE2B is partitioned among its many E3 partners and chain-type outputs (K48 degradative vs K63/monoubiquitin non-degradative) within a single cell remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unifying model for E3 partner selection in vivo\", \"Determinants of K48 vs K63 vs monoubiquitin output not defined\", \"Relative contribution of UBE2A vs UBE2B across pathways unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140096\", \"supporting_discovery_ids\": [5, 6, 9, 13]},\n      {\"term_id\": \"GO:0016874\", \"supporting_discovery_ids\": [5, 13, 14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [3, 9]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1, 10]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [2, 8, 11]},\n      {\"term_id\": \"R-HSA-162582\", \"supporting_discovery_ids\": [5, 6, 15]},\n      {\"term_id\": \"R-HSA-4839726\", \"supporting_discovery_ids\": [7, 9]}\n    ],\n    \"complexes\": [\n      \"RAD18-UBE2B (RAD6B) complex\"\n    ],\n    \"partners\": [\n      \"RAD18\",\n      \"UBR4\",\n      \"BIRC2\",\n      \"ZMYM2\",\n      \"CTNNB1\",\n      \"TRAF1\",\n      \"DNMT3a\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}