{"gene":"UIMC1","run_date":"2026-06-10T10:51:56","timeline":{"discoveries":[{"year":2007,"finding":"RAP80 contains tandem ubiquitin-interacting motifs (UIMs) that directly bind ubiquitin and K63-linked polyubiquitin chains at DNA double-strand breaks, and interacts with Abraxas (CCDC98) to form a BRCA1 complex (BRCA1-A complex) required for BRCA1 recruitment to DNA damage foci, G2/M checkpoint control, and DNA repair.","method":"Phosphopeptide affinity proteomics, co-immunoprecipitation, UIM domain deletion/mutation analysis, ionizing radiation-induced foci assays, siRNA knockdown with checkpoint and repair readouts","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — independently replicated by three simultaneous papers (PMID:17525340, 17525341, 17525342) using reciprocal Co-IP, domain deletion, and functional knockdown assays","pmids":["17525340","17525341","17525342"],"is_preprint":false},{"year":2007,"finding":"RAP80 recruits a complex containing BRCA1-BARD1 E3 ligase and the deubiquitinating enzyme BRCC36 to MDC1-γH2AX-dependent K6- and K63-linked ubiquitin polymers at DSBs; this complex assembly is required for cell cycle checkpoint and repair responses to ionizing radiation.","method":"Co-immunoprecipitation, ubiquitin chain-type specific binding assays, siRNA knockdown with checkpoint and foci readouts","journal":"Science","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal Co-IP plus functional knockdown, replicated across multiple papers","pmids":["17525341"],"is_preprint":false},{"year":2007,"finding":"RAP80 contains an Abraxas-interacting region (AIR) required for association with Abraxas, BRCA1, and BRCC36; Ubc13 (E2) and RNF8 (E3) generate K63-linked polyubiquitin chains at DNA damage sites that are recognized by RAP80 UIMs to recruit the entire BRCA1-A complex.","method":"Genetic knockdown (siRNA) of Ubc13/RNF8, domain mapping, co-immunoprecipitation, foci formation assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — epistasis (Ubc13/RNF8 required upstream of RAP80 foci), domain mapping, and multiple orthogonal methods; replicated across labs","pmids":["18077395"],"is_preprint":false},{"year":2009,"finding":"The tandem UIMs of RAP80 achieve K63-linked polyubiquitin selectivity through 'linkage-specific avidity': the inter-UIM linker positions UIM1 and UIM2 to simultaneously engage the proximal and distal ubiquitin moieties of a K63-linked di-ubiquitin, a geometry incompatible with K48-linked chains or monoubiquitin.","method":"In vitro ubiquitin binding assays, crystal structure of RAP80 tandem UIMs bound to K63-diubiquitin (2.2 Å), inter-UIM linker length mutants, pull-down analyses","journal":"Molecular Cell / The EMBO Journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — crystal structure at 2.2 Å (PMID:19536136) plus independent biochemical avidity model with mutagenesis (PMID:19328070); two orthogonal structural/biochemical approaches","pmids":["19328070","19536136"],"is_preprint":false},{"year":2009,"finding":"RAP80 and BRCC36 form a deubiquitinating enzyme (DUB) complex that antagonizes RNF8-Ubc13–dependent K63-ubiquitination at DSBs; BRCC36 knockdown or catalytically inactive mutant rescues 53BP1 and γH2AX ubiquitination levels following RNF8 depletion, establishing a steady-state balance of ubiquitin levels at DSBs.","method":"siRNA knockdown of BRCC36/RNF8, catalytically-inactive BRCC36 mutant expression, foci assays, ionizing radiation sensitivity assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 2 / Strong — active-site mutagenesis of BRCC36 combined with epistasis (RNF8/BRCC36 double knockdown), multiple readouts, replicated","pmids":["19202061"],"is_preprint":false},{"year":2009,"finding":"MERIT40 (C19orf62) is a RAP80-associated protein essential for BRCA1-RAP80 complex protein interactions, stability, and DSB targeting; MERIT40 is also required for RAP80-associated K63-ubiquitin DUB activity.","method":"Proteomic identification, co-immunoprecipitation, siRNA knockdown with foci and checkpoint readouts, DUB activity assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, functional siRNA knockdown with multiple orthogonal readouts (foci, DUB activity, checkpoint) in single lab","pmids":["19261746"],"is_preprint":false},{"year":2009,"finding":"The crystal structure and NMR solution structure of RAP80 tandem UIMs complexed with K63-linked di-ubiquitin show that UIM1 and UIM2 each contact the Ile44 hydrophobic patch of the proximal and distal ubiquitin moieties, respectively, and the inter-UIM region forms an alpha-helix that positions the two UIMs for linkage-specific binding.","method":"X-ray crystallography (2.2 Å), pull-down with inter-UIM mutants; NMR structure determination with NOE restraints and RDC data","journal":"The EMBO Journal / Journal of Biomolecular NMR","confidence":"High","confidence_rationale":"Tier 1 / Strong — two independent structural methods (crystal structure and NMR) with mutational validation","pmids":["19536136","22350954"],"is_preprint":false},{"year":2011,"finding":"The RAP80-BRCA1 complex suppresses excessive homologous recombination (HR) at DSBs by controlling the kinetics of HR-promoting BRCA1 complexes at nuclear foci; RAP80 depletion leads to exaggerated DSB end processing, elevated HR, and chromosomal instability.","method":"siRNA knockdown of RAP80, HR assays, foci kinetics by live imaging, chromosomal instability measurement","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal functional assays (HR frequency, end resection, chromosomal instability, foci kinetics), independently corroborated by PMID:21335604","pmids":["21406551","21335604"],"is_preprint":false},{"year":2011,"finding":"The BRCA1-RAP80 complex restricts Mre11-CtIP-dependent 5' end resection in S/G2 phase, thereby limiting HDR mechanisms that rely on 3' single-stranded overhangs; RAP80 or BRCC36 deficiency results in elevated end resection and increased HDR.","method":"siRNA knockdown, RPA/ssDNA foci assays, resection biochemical assays, HR reporter assays","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Moderate — two orthogonal readouts (resection assay and HDR reporter), consistent with PMID:21406551","pmids":["21335604"],"is_preprint":false},{"year":2010,"finding":"BRCC36 DUB activity within the RAP80 complex specifically requires Abraxas and BRCC45 interactions, distinct from its cytoplasmic BRISC complex where KIAA0157/Abro is required; BRISC deficiency enhances BRCA1-RAP80 complex formation and increases BRCA1 at DSBs.","method":"Co-immunoprecipitation, DUB activity assays, siRNA knockdown of complex components, foci assays","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — DUB activity assays with defined complex component requirements plus foci readout, single lab","pmids":["20656689"],"is_preprint":false},{"year":2012,"finding":"RAP80 contains a SUMO-interacting motif (SIM) that binds SUMO2/3 conjugates; together with the tandem UIMs, the SIM-UIM-UIM motif enables binding to both K63-ubiquitin and SUMO2 conjugates, and both SIM and UIM domains are required for efficient RAP80 recruitment to DSBs.","method":"SIM identification by sequence analysis, in vitro binding assays, co-immunoprecipitation, siRNA-rescue foci assays, IR sensitivity assays","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — two independent papers (PMID:22689573, PMID:23211528) using binding assays and functional rescue with domain mutants","pmids":["22689573","23211528"],"is_preprint":false},{"year":2012,"finding":"RNF4, a SUMO-targeted ubiquitin E3 ligase, synthesizes hybrid SUMO-ubiquitin chains at DSBs; RAP80 binds these hybrid chains through its SIM (nanomolar affinity) to promote BRCA1 recruitment; RNF4 depletion impairs RAP80 and BRCA1 foci formation.","method":"In vitro binding assays with hybrid SUMO-ubiquitin chains (affinity measurements), siRNA knockdown of RNF4 with foci readouts, co-immunoprecipitation","journal":"Science Signaling","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vitro affinity binding plus genetic knockdown with functional readout, demonstrates mechanistic connection between SUMO and ubiquitin pathways","pmids":["23211528"],"is_preprint":false},{"year":2015,"finding":"NMR structure of the SUMO-2·phospho-RAP80 SIM complex shows that CK2-dependent phosphorylation of the RAP80 SIM enhances affinity and specificity for SUMO-2 via electrostatic interactions with the isoform-specific SIM recognition module of SUMO-2.","method":"NMR spectroscopy, NMR structure determination, phosphopeptide binding assays","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure with phosphorylation-dependent affinity measurements, single lab but rigorous structural approach","pmids":["26719330"],"is_preprint":false},{"year":2007,"finding":"RAP80 directly interacts with estrogen receptor alpha (ERα) in an agonist-dependent manner through the hinge/LBD of ERα; RAP80 UIMs reduce ERα polyubiquitination and increase ERα protein levels and transcriptional activity; UIM deletion abolishes these effects without affecting ERα binding.","method":"Mammalian two-hybrid, GST pull-down, co-immunoprecipitation, siRNA knockdown, reporter assays, ubiquitination assays","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal co-IP and GST pull-down combined with functional UIM deletion assays, single lab","pmids":["17311814"],"is_preprint":false},{"year":2007,"finding":"RAP80 functions as an active transcriptional repressor and interacts with the retinoid-related testis-associated receptor (RTR) through its hinge domain; RAP80 competes with co-repressor N-CoR for RTR binding and inhibits RTR-N-CoR interaction.","method":"Mammalian two-hybrid, GST pull-down, co-immunoprecipitation, deletion/point mutation analysis, transcriptional reporter assays","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro pull-down plus co-IP plus functional transcriptional assays, single lab, single paper","pmids":["12080054"],"is_preprint":false},{"year":2007,"finding":"RAP80 is a target of SUMO-1 and SUMO-3 modification in intact cells; the SUMO-conjugating enzyme UBC9 interacts with RAP80 through residues 122–204; UBC9 overexpression enhances RAP80 mono- and multi-sumoylation.","method":"Yeast two-hybrid screen, co-immunoprecipitation, GST pull-down, in vivo sumoylation assays","journal":"Biochemical and Biophysical Research Communications","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP and in-cell sumoylation assays, single lab, multiple methods but no functional consequence established","pmids":["17698038"],"is_preprint":false},{"year":2009,"finding":"ATM phosphorylates RAP80 at Ser205 in cells exposed to ionizing radiation within 5 minutes after irradiation; UV irradiation induces RAP80 Ser205 phosphorylation via ATR (not ATM); this phosphorylation is not required for IRIF formation.","method":"Phospho-specific antibody generation, ATM/ATR inhibitor treatment, immunofluorescence, kinase assays","journal":"Cancer Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phospho-specific antibody validated with ATM inhibitors plus in vitro kinase assay (PMID:17621610 and 18519686), single lab","pmids":["18519686","17621610"],"is_preprint":false},{"year":2009,"finding":"RAP80 interacts with p53 and the E3 ubiquitin ligase HDM2 to promote HDM2-dependent p53 polyubiquitination; RAP80 is transcriptionally induced by p53 in a DNA-damage-responsive manner through a noncanonical p53 response element, forming an autoregulatory loop.","method":"Promoter analysis, co-immunoprecipitation, ubiquitination assays, siRNA knockdown with p53 target gene and apoptosis readouts","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP for protein interaction, in vivo ubiquitination assay, promoter reporter assay, functional siRNA knockdown; single lab","pmids":["19433585"],"is_preprint":false},{"year":2012,"finding":"RAP80 protein levels fluctuate during the cell cycle; RAP80 is degraded by APC/C(Cdc20) during mitosis and APC/C(Cdh1) during G1 phase through a conserved destruction box (D-box); knockdown of Cdc20 or Cdh1 blocks RAP80 degradation; overexpression of a D-box deletion mutant attenuates mitotic progression.","method":"Cell cycle synchronization, flow cytometry, siRNA knockdown of Cdc20/Cdh1, ubiquitination assays, D-box mutant expression","journal":"Molecular Cancer Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — D-box mutagenesis, siRNA of specific E3 components, and functional mitotic progression readout; single lab","pmids":["22426463"],"is_preprint":false},{"year":2012,"finding":"Cdk1-cyclin B1 complex phosphorylates RAP80 at Ser677; this phosphorylation occurs in M phase and is induced by ionizing radiation; Ser677Ala mutation sensitizes cells to IR and impairs G2/M checkpoint control.","method":"In vitro kinase assay, phosphopeptide-specific antibody, Ser677Ala mutant expression, IR sensitivity assays, G2/M checkpoint assays","journal":"The Journal of Biological Chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — in vitro kinase assay with phospho-specific antibody validation and functional mutant analysis; single lab","pmids":["23264621"],"is_preprint":false},{"year":2011,"finding":"MDC1 directly binds RAP80 through its tandem BRCT domain and the UIMs of RAP80; this interaction depends on UBC13-dependent ubiquitylation of MDC1 at K1977; K1977 of MDC1 is required for RAP80 focus formation at DSBs.","method":"Co-immunoprecipitation, direct binding assay, UBC13 knockdown, MDC1 K1977 mutagenesis, foci assays","journal":"DNA Repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding demonstrated with domain mapping, ubiquitination-dependence shown by E2 knockdown and site mutagenesis; single lab","pmids":["21622030"],"is_preprint":false},{"year":2012,"finding":"RAP80 acts as a scaffold protein for the BRCA1-A complex; loss of RAP80 (in RAP80-null TOV-21G cells) disrupts the entire complex and suppresses recruitment of BRCA1, CCDC98, NBA1, BRCC36 and BRE to DSBs; reconstitution with wild-type RAP80 rescues these defects.","method":"RAP80-null cell line identification, co-immunoprecipitation, foci assays, reconstitution experiments, IR sensitivity assay","journal":"PloS ONE","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reconstitution in null cell line with multiple complex component readouts; single lab","pmids":["22792303"],"is_preprint":false},{"year":2012,"finding":"RAP80-deficient mice develop B-cell lymphomas with clonal chromosomal translocations and are hypersensitive to ionizing radiation; RAP80-null MEFs show impaired DSB repair due to loss of BRCA1-A complex recruitment to damage sites.","method":"RAP80 knockout mouse generation, tumor surveillance, IR sensitivity assays, γH2AX/foci assays in MEFs","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — germline knockout with multiple in vivo and cellular phenotypic readouts; corroborated by independent RAP80-null mouse study (PMID:22896338)","pmids":["22539352","22896338"],"is_preprint":false},{"year":2015,"finding":"USP26 and USP37 are recruited to DSBs where they remove RNF168-induced ubiquitin conjugates, limiting RAP80-BRCA1 spreading from DSBs; their depletion impairs HR, and this defect is rescued by simultaneous RAP80 depletion, placing USP26/USP37 as antagonists of RAP80-mediated BRCA1 sequestration.","method":"Genetic screen, siRNA knockdown epistasis (single and double depletions), foci assays, HR reporter assays","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis (double depletion rescue) combined with foci and HR functional readouts; single lab","pmids":["26101254"],"is_preprint":false},{"year":2015,"finding":"TIP60-mediated H4K16 acetylation prevents 53BP1 binding to H4K20me2; Fanconi anemia pathway inactivation impairs FANCD2 monoubiquitination and TIP60 relocalization, leading to aberrant chromatin accumulation of RAP80 and 53BP1 that impairs resection and HR.","method":"siRNA knockdown, ChIP, histone modification analysis, HR assays","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pathway epistasis through siRNA and chromatin assays; single lab; RAP80 is one of several readouts","pmids":["26446986"],"is_preprint":false},{"year":2016,"finding":"TRAIP/RNF206 is a novel RAP80-interacting protein that acts upstream of RAP80; TRAIP depletion impairs RAP80 and BRCA1 accumulation at DNA lesions; TRAIP localizes to damage sites through direct interaction with RNF20-RNF40 via its C-terminus, while its N-terminus mediates RAP80 binding.","method":"Co-immunoprecipitation, siRNA knockdown with foci readouts, domain mapping, in vitro binding assays","journal":"Nature Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — Co-IP with domain mapping, siRNA epistasis showing TRAIP upstream of RAP80; single lab","pmids":["26781088"],"is_preprint":false},{"year":2017,"finding":"USP13 is phosphorylated by ATM following DNA damage and deubiquitinates RAP80, promoting RAP80 recruitment to DSBs and proper DDR; USP13 depletion or inhibition sensitizes ovarian cancer cells to cisplatin and PARP inhibitors.","method":"Co-immunoprecipitation, in vitro deubiquitination assays, ATM inhibitor treatment, siRNA knockdown, foci assays, drug sensitivity assays","journal":"Nature Communications","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro DUB assay and Co-IP with ATM-dependent phosphorylation and functional drug sensitivity readout; single lab","pmids":["28569838"],"is_preprint":false},{"year":2009,"finding":"The inter-UIM linker length of RAP80 is a critical determinant of K63-linked polyubiquitin binding affinity; modifying linker length by insertion or deletion changes binding affinity and impairs translocation to DSBs.","method":"In vitro GST pull-down assays with linker mutants, foci assays","journal":"BMB Reports","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, in vitro pull-down only; consistent with structural data but no in vivo mechanistic follow-up","pmids":["19944020"],"is_preprint":false},{"year":2009,"finding":"The RAP80 ΔE81 deletion mutant (c.241-243delGAA) found in familial breast cancer cases displays significantly reduced ubiquitin binding and DSB localization, impairs BRCA1 and Abraxas DSB recruitment, and increases chromosomal aberrations.","method":"Ubiquitin binding assays, foci formation assays, chromosomal aberration analysis, expression of ΔE81 allele","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — functional domain mutation with multiple readouts (ubiquitin binding, foci, chromosomal aberrations); single lab; mechanism confirmed by structural studies (PMID:24627472)","pmids":["19305427","24627472"],"is_preprint":false},{"year":2014,"finding":"NMR spectroscopy shows that the ΔE81 deletion causes a structural frameshift in the N-cap of the first UIM alpha-helix, abolishing multivalent polyubiquitin binding by disrupting favorable electrostatic interactions between UIM1 and ubiquitin.","method":"NMR spectroscopy, structural comparison of wild-type and ΔE81 UIM1","journal":"The Journal of Biological Chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structural determination with mechanistic explanation of binding loss; single lab but rigorous structural approach","pmids":["24627472"],"is_preprint":false},{"year":2020,"finding":"BRCA1 PARsylation and RAP80-bound BRCA1 together regulate normal interaction of BRCA1 with CtIP and BACH1 in nuclear foci; simultaneous loss of RAP80 and failure of BRCA1 PARsylation results in dysregulated accumulation of BRCA1 complexes in foci, hyper-recombination, and gross chromosomal disorder.","method":"Genetic depletion (siRNA/knockout), PARP inhibition, HR assays, foci kinetics, chromosomal instability measurement","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — double loss-of-function genetic analysis with multiple readouts; single lab","pmids":["31932421"],"is_preprint":false},{"year":2014,"finding":"FANCG undergoes K63-linked polyubiquitination in response to DNA damage, which is required for its interaction with the RAP80-BRCA1 complex and subsequent HR repair of ICLs; BRCC36 deubiquitinates K63-ubiquitinated FANCG in vitro and in vivo.","method":"Co-immunoprecipitation, in vitro ubiquitination/deubiquitination assays, FANCG 3KR mutant expressing cells, HR reporter assays","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro deubiquitination assay plus Co-IP with functional mutant analysis; single lab","pmids":["25132264"],"is_preprint":false},{"year":2017,"finding":"RAP80 binds the mitochondrial protein p32 through its arginine-rich C-terminal domain; a subset of RAP80 localizes to mitochondria; RAP80 deficiency reduces p32 protein levels and p32-dependent mitochondrial proteins (Rieske, COX1), reducing mitochondrial membrane potential and oxygen consumption.","method":"Yeast two-hybrid screening, co-immunoprecipitation, subcellular fractionation/mitochondrial localization, siRNA knockdown with mitochondrial function readouts","journal":"Biochemical and Biophysical Research Communications","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single lab, Co-IP plus fractionation without rigorous mechanistic follow-up; novel localization claim with limited supporting data","pmids":["28842250"],"is_preprint":false},{"year":2022,"finding":"RAP80 prevents CtIP-mediated nucleolytic processing of ssDNA in R-loops near DSBs, thereby promoting efficient DSB repair via transcription-associated end joining dependent on BRCA1, Polθ, and LIG1/3; RAP80 depletion increases chromosome translocations and deletions due to unscheduled R-loop ssDNA processing.","method":"siRNA knockdown, R-loop detection (S9.6 immunofluorescence), CtIP epistasis, chromosomal translocation and deletion assays","journal":"Cell Reports","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis (double depletion of RAP80 and CtIP), R-loop detection, and chromosomal instability readouts; single lab","pmids":["35108530"],"is_preprint":false},{"year":2023,"finding":"RAP80 undergoes liquid-liquid phase separation (LLPS) at DSBs through an intrinsically disordered region (IDR) at its N-terminus; K63-linked polyubiquitin chains at DSBs strongly enhance RAP80 phase separation; abolishing RAP80 condensation suppresses BRCA1 foci formation and increases radiosensitivity.","method":"In vitro phase separation assays, cellular condensate imaging, IDR deletion mutants, radiosensitivity assays","journal":"Nucleic Acids Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and cellular LLPS assays with IDR mutants and functional readout; single lab","pmids":["37638744"],"is_preprint":false},{"year":2024,"finding":"DOT1L methyltransferase is recruited to chromatin after DNA damage and methylates RAP80 at multiple lysines; methylated RAP80 binds ubiquitinated H2A and triggers BRCA1-A complex recruitment to DSBs; DOT1L inhibition or mutation of RAP80 methylation sites reduces BRCA1 recruitment and enhances radiosensitivity.","method":"In vitro methylation assays, methylation site identification by MS, Co-IP, ChIP, ubiquitinated H2A pull-down, siRNA/inhibitor knockdown with foci and radiosensitivity readouts","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro methylation assay plus functional Co-IP and pull-down showing methylation-dependent H2A binding; single lab","pmids":["39172790"],"is_preprint":false},{"year":2010,"finding":"RAP80 performs a BRCA1-independent repair function specific to topoisomerase II inhibitor (etoposide) damage; RAP80-null DT40 cells are proficient in HR and NHEJ but sensitive to etoposide; RAP80/BRCA1 double knockout cells are more sensitive to etoposide than BRCA1 single knockouts.","method":"Genetic disruption of RAP80 in DT40 cells, single and double mutant analysis, drug sensitivity assays (etoposide, other agents), HR and NHEJ assays","journal":"Cancer Research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic KO with epistasis (double mutant more sensitive), multiple DNA damage agent readouts; single lab","pmids":["20959489"],"is_preprint":false},{"year":2026,"finding":"SENP3 deSUMOylates RAP80 to facilitate timely RAP80 dissociation from DSB sites during later stages of repair; SENP3 depletion causes aberrant prolonged RAP80 SUMOylation and retention at damage foci, impairing HR repair progression.","method":"Co-immunoprecipitation, in vivo SUMOylation assays, siRNA knockdown of SENP3, foci assays, HR and IR sensitivity assays","journal":"Acta Biochimica et Biophysica Sinica","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single recent paper, Co-IP and in-vivo sumoylation assays, no structural or in vitro reconstitution data; functional consequence plausible but single lab single method","pmids":["42093510"],"is_preprint":false}],"current_model":"RAP80 (UIMC1) is a multivalent ubiquitin/SUMO receptor that forms the core of the BRCA1-A complex: its tandem UIMs bind K63-linked polyubiquitin chains generated by the RNF8-Ubc13 cascade at DSBs (with selectivity arising from linkage-specific avidity enforced by the inter-UIM helical linker), while an upstream SIM binds SUMO-2/3 and hybrid SUMO-ubiquitin chains synthesized by RNF4, together recruiting the Abraxas–BRCC36–MERIT40–BRCA1–BARD1 complex to break sites; paradoxically, rather than solely promoting homologous recombination, the RAP80-BRCA1 complex actively suppresses excessive HR by restraining CtIP-dependent end resection and sequestering BRCA1 away from PALB2-BRCA2-RAD51, thereby tuning the balance between competing repair pathways; RAP80 undergoes multiple post-translational modifications (ATM/ATR phosphorylation at Ser205, Cdk1 phosphorylation at Ser677, CK2 phosphorylation of the SIM, K63-ubiquitination reversed by USP13, SUMOylation reversed by SENP3, DOT1L-mediated methylation enabling H2AX binding, and APC/C-dependent proteasomal degradation during mitosis/G1) that collectively regulate its activity and abundance throughout the cell cycle, while its intrinsically disordered region drives phase separation at DSBs to concentrate BRCA1 recruitment."},"narrative":{"mechanistic_narrative":"RAP80 (UIMC1) is a multivalent ubiquitin/SUMO receptor that nucleates the BRCA1-A complex at DNA double-strand breaks (DSBs) and governs the magnitude of the DNA damage response [PMID:17525340, PMID:17525341, PMID:17525342, PMID:22792303]. Its tandem ubiquitin-interacting motifs (UIMs) selectively recognize K63-linked polyubiquitin chains generated by the RNF8-Ubc13 cascade, with linkage specificity arising from an inter-UIM helical linker that positions the two UIMs to simultaneously engage the proximal and distal ubiquitin moieties of K63 di-ubiquitin [PMID:18077395, PMID:19328070, PMID:19536136, PMID:22350954]. A complementary SUMO-interacting motif (SIM) binds SUMO-2/3 and the hybrid SUMO-ubiquitin chains synthesized by RNF4, and CK2-dependent phosphorylation of the SIM enhances its affinity for SUMO-2; both SIM and UIM modules are required for efficient RAP80 recruitment to breaks [PMID:22689573, PMID:23211528, PMID:26719330]. Through an Abraxas-interacting region, RAP80 assembles and stabilizes the Abraxas-BRCC36-MERIT40-BRCA1-BARD1 complex, in which the BRCC36 deubiquitinase counterbalances RNF8-Ubc13 ubiquitination to set a steady-state ubiquitin level at breaks [PMID:17525340, PMID:17525341, PMID:17525342, PMID:19202061, PMID:19261746, PMID:22792303]. Functionally, the RAP80-BRCA1 complex restrains rather than simply promotes repair: it limits Mre11-CtIP-dependent end resection and suppresses excessive homologous recombination, and its loss causes hyper-resection, elevated HR, and chromosomal instability [PMID:21406551, PMID:21335604]. RAP80 activity and abundance are tuned across the cell cycle by ATM/ATR phosphorylation at Ser205, Cdk1 phosphorylation at Ser677, USP13-reversed ubiquitination, DOT1L-mediated methylation that enables binding to ubiquitinated H2A, and APC/C-dependent destruction-box proteolysis in mitosis and G1 [PMID:18519686, PMID:17621610, PMID:22426463, PMID:23264621, PMID:28569838, PMID:39172790]. Its N-terminal intrinsically disordered region drives K63-polyubiquitin-stimulated liquid-liquid phase separation that concentrates BRCA1 recruitment at breaks [PMID:37638744]. RAP80 is a tumor suppressor in vivo, as RAP80-deficient mice develop B-cell lymphomas with clonal translocations, and a familial breast-cancer ΔE81 allele disrupts UIM1 structure and ubiquitin binding to impair complex recruitment [PMID:22539352, PMID:22896338, PMID:19305427, PMID:24627472].","teleology":[{"year":2007,"claim":"Established RAP80 as the ubiquitin sensor that links K63-polyubiquitin at breaks to BRCA1 recruitment, defining the BRCA1-A complex and its checkpoint/repair role.","evidence":"Phosphopeptide affinity proteomics, reciprocal Co-IP, UIM mutagenesis, and IR-induced foci/checkpoint assays across three simultaneous papers","pmids":["17525340","17525341","17525342"],"confidence":"High","gaps":["Did not resolve the structural basis of K63 selectivity","Upstream E3/E2 generating the chains not yet defined here"]},{"year":2007,"claim":"Identified the upstream RNF8-Ubc13 cascade and the Abraxas-interacting region, placing RAP80 downstream of MDC1-γH2AX-dependent ubiquitination.","evidence":"siRNA epistasis of Ubc13/RNF8, domain mapping, and foci assays","pmids":["18077395","17525341"],"confidence":"High","gaps":["Did not address how RAP80 modulates resection or HR outcome","Stoichiometry of complex assembly unresolved"]},{"year":2009,"claim":"Defined the structural mechanism of K63 linkage selectivity through tandem-UIM avidity enforced by the inter-UIM helical linker.","evidence":"2.2 Å crystal structure and NMR of tandem UIMs bound to K63 di-ubiquitin with linker-length mutants","pmids":["19328070","19536136","22350954"],"confidence":"High","gaps":["Did not address SUMO-chain recognition","In vivo consequence of altered linker only partially tested"]},{"year":2009,"claim":"Showed RAP80 builds a DUB-active complex with BRCC36 and MERIT40 that antagonizes RNF8-Ubc13 ubiquitination, balancing ubiquitin levels at breaks.","evidence":"Catalytically inactive BRCC36 mutants, RNF8/BRCC36 epistasis, and complex-component knockdowns with foci/DUB readouts","pmids":["19202061","19261746"],"confidence":"High","gaps":["Physiological substrates of the DUB at breaks incompletely defined","Quantitative balance point not measured"]},{"year":2011,"claim":"Reframed RAP80-BRCA1 as a restraint on repair, showing it limits CtIP-Mre11 end resection and suppresses excessive HR to preserve genome stability.","evidence":"RAP80/BRCC36 knockdown with HR reporters, RPA/ssDNA resection assays, foci kinetics, and chromosomal instability measurements","pmids":["21406551","21335604","21622030"],"confidence":"High","gaps":["Molecular mechanism by which complex blocks resection not fully defined","Relationship to BRCA1 partitioning toward PALB2-BRCA2 not directly tested here"]},{"year":2012,"claim":"Added a SUMO arm: a SIM binds SUMO-2/3 and RNF4-made hybrid SUMO-ubiquitin chains, and both SIM and UIMs are needed for recruitment, integrating SUMO and ubiquitin signaling.","evidence":"In vitro affinity binding to hybrid chains, RNF4 knockdown, and SIM/UIM rescue foci assays","pmids":["22689573","23211528"],"confidence":"High","gaps":["Relative contribution of SUMO vs ubiquitin reading in vivo unquantified","Identity of the SUMOylated substrates at breaks unclear"]},{"year":2012,"claim":"Established cell-cycle control of RAP80 abundance and activity via APC/C destruction-box proteolysis and Cdk1 Ser677 phosphorylation.","evidence":"Synchronization, Cdc20/Cdh1 knockdown, D-box mutants, in vitro Cdk1 kinase assays, and G2/M checkpoint readouts","pmids":["22426463","23264621"],"confidence":"Medium","gaps":["Interplay between degradation and modification not integrated","Functional impact of fluctuation on repair timing not directly tested"]},{"year":2012,"claim":"Confirmed RAP80 as the scaffold whose loss collapses BRCA1-A complex recruitment, validated in a RAP80-null human line by reconstitution.","evidence":"RAP80-null TOV-21G cells, Co-IP, foci of complex components, and wild-type rescue","pmids":["22792303"],"confidence":"Medium","gaps":["Single cell-line context","Quantitative scaffolding contributions of individual subunits unresolved"]},{"year":2012,"claim":"Demonstrated RAP80 is a tumor suppressor in vivo, with knockout mice developing lymphomas and IR hypersensitivity from defective complex recruitment.","evidence":"Germline knockout mice, tumor surveillance, IR sensitivity, and γH2AX/foci assays in MEFs, corroborated by an independent knockout","pmids":["22539352","22896338"],"confidence":"High","gaps":["Tissue specificity of tumor predisposition not mechanistically explained","Contribution of HR suppression vs other functions to tumorigenesis unresolved"]},{"year":2014,"claim":"Provided the structural explanation for a familial breast-cancer allele, showing ΔE81 frameshifts the UIM1 N-cap and abolishes multivalent ubiquitin binding.","evidence":"NMR comparison of wild-type and ΔE81 UIM1 with ubiquitin-binding and foci assays","pmids":["24627472","19305427"],"confidence":"High","gaps":["Disease causality at the population level not established by structure alone","Penetrance and modifier effects unaddressed"]},{"year":2015,"claim":"Defined antagonistic DUBs (USP26/USP37) that limit RAP80-BRCA1 spreading, and CK2 phosphorylation enhancing SIM-SUMO-2 specificity.","evidence":"Genetic screen with double-depletion rescue, foci/HR assays, and NMR of SUMO-2·phospho-SIM complex","pmids":["26101254","26719330"],"confidence":"Medium","gaps":["Coordination of these regulators in vivo not integrated","Temporal sequence of phospho-SIM activation during repair unclear"]},{"year":2017,"claim":"Identified USP13 as an ATM-activated DUB that deubiquitinates RAP80 to promote its recruitment, with therapeutic relevance to PARP/cisplatin sensitivity.","evidence":"In vitro DUB assays, ATM-dependent phosphorylation, Co-IP, foci, and drug sensitivity assays","pmids":["28569838"],"confidence":"Medium","gaps":["Specific RAP80 ubiquitination sites reversed by USP13 not mapped","Single lab"]},{"year":2022,"claim":"Extended RAP80 function to R-loop protection, preventing CtIP processing of R-loop ssDNA near breaks to enable transcription-associated end joining.","evidence":"siRNA knockdown, S9.6 R-loop imaging, CtIP epistasis, and translocation/deletion assays","pmids":["35108530"],"confidence":"Medium","gaps":["Direct RAP80 binding to R-loop structures not shown","Mechanism of CtIP restriction at R-loops unresolved"]},{"year":2023,"claim":"Showed RAP80 IDR-driven, K63-polyubiquitin-stimulated phase separation concentrates BRCA1 recruitment at breaks.","evidence":"In vitro phase separation, cellular condensate imaging, IDR deletion mutants, and radiosensitivity assays","pmids":["37638744"],"confidence":"Medium","gaps":["In vivo necessity of condensation distinct from binding not fully separated","Single lab"]},{"year":2024,"claim":"Added a methylation layer: DOT1L methylates RAP80 to enable binding of ubiquitinated H2A and BRCA1-A recruitment.","evidence":"In vitro methylation, MS site mapping, ubiquitinated-H2A pull-down, ChIP, and foci/radiosensitivity assays","pmids":["39172790"],"confidence":"Medium","gaps":["Interplay of methylation with UIM/SIM reading not integrated","Single lab"]},{"year":null,"claim":"How RAP80's multiple, partly redundant recruitment modes (UIM, SIM, methyl-H2A reading, phase separation) and its many post-translational modifications are quantitatively coordinated in time to switch BRCA1-A from HR restraint to other repair functions remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified kinetic model integrating modifications and recruitment modes","Relative contributions of SUMO vs ubiquitin vs methylation reading not partitioned in vivo","Mechanism linking HR restraint to alternative end-joining/R-loop functions unclear"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0060090","term_label":"molecular adaptor 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Specifically recognizes and binds 'Lys-63'-linked ubiquitin (PubMed:19328070, Ref.38). Plays a central role in the BRCA1-A complex by specifically binding 'Lys-63'-linked ubiquitinated histones H2A and H2AX at DNA lesions sites, leading to target the BRCA1-BARD1 heterodimer to sites of DNA damage at double-strand breaks (DSBs). The BRCA1-A complex also possesses deubiquitinase activity that specifically removes 'Lys-63'-linked ubiquitin on histones H2A and H2AX. Also weakly binds monoubiquitin but with much less affinity than 'Lys-63'-linked ubiquitin. May interact with monoubiquitinated histones H2A and H2B; the relevance of such results is however unclear in vivo. Does not bind Lys-48'-linked ubiquitin. May indirectly act as a transcriptional repressor by inhibiting the interaction of NR6A1 with the corepressor NCOR1","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q96RL1/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/UIMC1","classification":"Not Classified","n_dependent_lines":15,"n_total_lines":1208,"dependency_fraction":0.012417218543046357},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/UIMC1","total_profiled":1310},"omim":[{"mim_id":"618650","title":"RING FINGER PROTEIN 169; RNF169","url":"https://www.omim.org/entry/618650"},{"mim_id":"617883","title":"FANCONI ANEMIA, COMPLEMENTATION GROUP S; FANCS","url":"https://www.omim.org/entry/617883"},{"mim_id":"612886","title":"MENOPAUSE, NATURAL, AGE AT, QUANTITATIVE TRAIT LOCUS 4; 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all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/UIMC1"},"hgnc":{"alias_symbol":["RAP80"],"prev_symbol":[]},"alphafold":{"accession":"Q96RL1","domains":[{"cath_id":"1.20.5","chopping":"81-115","consensus_level":"medium","plddt":95.678,"start":81,"end":115}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96RL1","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96RL1-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96RL1-F1-predicted_aligned_error_v6.png","plddt_mean":55.41},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=UIMC1","jax_strain_url":"https://www.jax.org/strain/search?query=UIMC1"},"sequence":{"accession":"Q96RL1","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96RL1.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96RL1/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96RL1"}},"corpus_meta":[{"pmid":"17525340","id":"PMC_17525340","title":"Abraxas and RAP80 form a BRCA1 protein 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one","url":"https://pubmed.ncbi.nlm.nih.gov/24039796","citation_count":6,"is_preprint":false},{"pmid":"30705591","id":"PMC_30705591","title":"RAP80 expression in breast cancer and its relationship with apoptosis in breast cancer cells.","date":"2019","source":"OncoTargets and therapy","url":"https://pubmed.ncbi.nlm.nih.gov/30705591","citation_count":6,"is_preprint":false},{"pmid":"30008919","id":"PMC_30008919","title":"Association between EGFR mutation and expression of BRCA1 and RAP80 in non-small cell lung cancer.","date":"2018","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/30008919","citation_count":6,"is_preprint":false},{"pmid":"17562356","id":"PMC_17562356","title":"RAP80/UIMC1 as cancer-associated antigen: alternative splice variants and their immunogenicity.","date":"2007","source":"Cancer letters","url":"https://pubmed.ncbi.nlm.nih.gov/17562356","citation_count":5,"is_preprint":false},{"pmid":"22573342","id":"PMC_22573342","title":"Induction of pancreatic cancer cell apoptosis and enhancement of gemcitabine sensitivity by RAP80 siRNA.","date":"2012","source":"Digestive diseases and sciences","url":"https://pubmed.ncbi.nlm.nih.gov/22573342","citation_count":4,"is_preprint":false},{"pmid":"28842250","id":"PMC_28842250","title":"RAP80 binds p32 to preserve the functional integrity of mitochondria.","date":"2017","source":"Biochemical and biophysical research communications","url":"https://pubmed.ncbi.nlm.nih.gov/28842250","citation_count":4,"is_preprint":false},{"pmid":"42093510","id":"PMC_42093510","title":"SENP3 regulates DNA damage repair by downregulating RAP80 SUMOylation.","date":"2026","source":"Acta biochimica et biophysica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/42093510","citation_count":0,"is_preprint":false},{"pmid":"27443420","id":"PMC_27443420","title":"Low RAP80 mRNA expression correlates with shorter survival in sporadic high-grade serous ovarian carcinoma.","date":"2017","source":"The International journal of biological markers","url":"https://pubmed.ncbi.nlm.nih.gov/27443420","citation_count":0,"is_preprint":false},{"pmid":"27998448","id":"PMC_27998448","title":"[Chinese multicenter randomized trial of customized chemotherapy based on BRCA1 (breast cancer susceptibility gene 1)-RAP80 (receptor-associated protein 80) mRNA expression in advanced non-small cell lung cancer (NSCLC) patients].","date":"2016","source":"Zhonghua zhong liu za zhi [Chinese journal of oncology]","url":"https://pubmed.ncbi.nlm.nih.gov/27998448","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.06.10.658793","title":"HSV-1 orchestrates host RAP80 ubiquitination by ICP0 and UL36USP to promote viral survival","date":"2025-06-11","source":"bioRxiv","url":"https://doi.org/10.1101/2025.06.10.658793","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":29996,"output_tokens":9312,"usd":0.114834,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":19403,"output_tokens":4934,"usd":0.110183,"stage2_stop_reason":"end_turn"},"total_usd":0.225017,"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\": 2007,\n      \"finding\": \"RAP80 contains tandem ubiquitin-interacting motifs (UIMs) that directly bind ubiquitin and K63-linked polyubiquitin chains at DNA double-strand breaks, and interacts with Abraxas (CCDC98) to form a BRCA1 complex (BRCA1-A complex) required for BRCA1 recruitment to DNA damage foci, G2/M checkpoint control, and DNA repair.\",\n      \"method\": \"Phosphopeptide affinity proteomics, co-immunoprecipitation, UIM domain deletion/mutation analysis, ionizing radiation-induced foci assays, siRNA knockdown with checkpoint and repair readouts\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — independently replicated by three simultaneous papers (PMID:17525340, 17525341, 17525342) using reciprocal Co-IP, domain deletion, and functional knockdown assays\",\n      \"pmids\": [\"17525340\", \"17525341\", \"17525342\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAP80 recruits a complex containing BRCA1-BARD1 E3 ligase and the deubiquitinating enzyme BRCC36 to MDC1-γH2AX-dependent K6- and K63-linked ubiquitin polymers at DSBs; this complex assembly is required for cell cycle checkpoint and repair responses to ionizing radiation.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitin chain-type specific binding assays, siRNA knockdown with checkpoint and foci readouts\",\n      \"journal\": \"Science\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal Co-IP plus functional knockdown, replicated across multiple papers\",\n      \"pmids\": [\"17525341\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAP80 contains an Abraxas-interacting region (AIR) required for association with Abraxas, BRCA1, and BRCC36; Ubc13 (E2) and RNF8 (E3) generate K63-linked polyubiquitin chains at DNA damage sites that are recognized by RAP80 UIMs to recruit the entire BRCA1-A complex.\",\n      \"method\": \"Genetic knockdown (siRNA) of Ubc13/RNF8, domain mapping, co-immunoprecipitation, foci formation assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — epistasis (Ubc13/RNF8 required upstream of RAP80 foci), domain mapping, and multiple orthogonal methods; replicated across labs\",\n      \"pmids\": [\"18077395\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The tandem UIMs of RAP80 achieve K63-linked polyubiquitin selectivity through 'linkage-specific avidity': the inter-UIM linker positions UIM1 and UIM2 to simultaneously engage the proximal and distal ubiquitin moieties of a K63-linked di-ubiquitin, a geometry incompatible with K48-linked chains or monoubiquitin.\",\n      \"method\": \"In vitro ubiquitin binding assays, crystal structure of RAP80 tandem UIMs bound to K63-diubiquitin (2.2 Å), inter-UIM linker length mutants, pull-down analyses\",\n      \"journal\": \"Molecular Cell / The EMBO Journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — crystal structure at 2.2 Å (PMID:19536136) plus independent biochemical avidity model with mutagenesis (PMID:19328070); two orthogonal structural/biochemical approaches\",\n      \"pmids\": [\"19328070\", \"19536136\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RAP80 and BRCC36 form a deubiquitinating enzyme (DUB) complex that antagonizes RNF8-Ubc13–dependent K63-ubiquitination at DSBs; BRCC36 knockdown or catalytically inactive mutant rescues 53BP1 and γH2AX ubiquitination levels following RNF8 depletion, establishing a steady-state balance of ubiquitin levels at DSBs.\",\n      \"method\": \"siRNA knockdown of BRCC36/RNF8, catalytically-inactive BRCC36 mutant expression, foci assays, ionizing radiation sensitivity assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — active-site mutagenesis of BRCC36 combined with epistasis (RNF8/BRCC36 double knockdown), multiple readouts, replicated\",\n      \"pmids\": [\"19202061\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"MERIT40 (C19orf62) is a RAP80-associated protein essential for BRCA1-RAP80 complex protein interactions, stability, and DSB targeting; MERIT40 is also required for RAP80-associated K63-ubiquitin DUB activity.\",\n      \"method\": \"Proteomic identification, co-immunoprecipitation, siRNA knockdown with foci and checkpoint readouts, DUB activity assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, functional siRNA knockdown with multiple orthogonal readouts (foci, DUB activity, checkpoint) in single lab\",\n      \"pmids\": [\"19261746\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The crystal structure and NMR solution structure of RAP80 tandem UIMs complexed with K63-linked di-ubiquitin show that UIM1 and UIM2 each contact the Ile44 hydrophobic patch of the proximal and distal ubiquitin moieties, respectively, and the inter-UIM region forms an alpha-helix that positions the two UIMs for linkage-specific binding.\",\n      \"method\": \"X-ray crystallography (2.2 Å), pull-down with inter-UIM mutants; NMR structure determination with NOE restraints and RDC data\",\n      \"journal\": \"The EMBO Journal / Journal of Biomolecular NMR\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — two independent structural methods (crystal structure and NMR) with mutational validation\",\n      \"pmids\": [\"19536136\", \"22350954\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The RAP80-BRCA1 complex suppresses excessive homologous recombination (HR) at DSBs by controlling the kinetics of HR-promoting BRCA1 complexes at nuclear foci; RAP80 depletion leads to exaggerated DSB end processing, elevated HR, and chromosomal instability.\",\n      \"method\": \"siRNA knockdown of RAP80, HR assays, foci kinetics by live imaging, chromosomal instability measurement\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal functional assays (HR frequency, end resection, chromosomal instability, foci kinetics), independently corroborated by PMID:21335604\",\n      \"pmids\": [\"21406551\", \"21335604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"The BRCA1-RAP80 complex restricts Mre11-CtIP-dependent 5' end resection in S/G2 phase, thereby limiting HDR mechanisms that rely on 3' single-stranded overhangs; RAP80 or BRCC36 deficiency results in elevated end resection and increased HDR.\",\n      \"method\": \"siRNA knockdown, RPA/ssDNA foci assays, resection biochemical assays, HR reporter assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal readouts (resection assay and HDR reporter), consistent with PMID:21406551\",\n      \"pmids\": [\"21335604\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"BRCC36 DUB activity within the RAP80 complex specifically requires Abraxas and BRCC45 interactions, distinct from its cytoplasmic BRISC complex where KIAA0157/Abro is required; BRISC deficiency enhances BRCA1-RAP80 complex formation and increases BRCA1 at DSBs.\",\n      \"method\": \"Co-immunoprecipitation, DUB activity assays, siRNA knockdown of complex components, foci assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — DUB activity assays with defined complex component requirements plus foci readout, single lab\",\n      \"pmids\": [\"20656689\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RAP80 contains a SUMO-interacting motif (SIM) that binds SUMO2/3 conjugates; together with the tandem UIMs, the SIM-UIM-UIM motif enables binding to both K63-ubiquitin and SUMO2 conjugates, and both SIM and UIM domains are required for efficient RAP80 recruitment to DSBs.\",\n      \"method\": \"SIM identification by sequence analysis, in vitro binding assays, co-immunoprecipitation, siRNA-rescue foci assays, IR sensitivity assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — two independent papers (PMID:22689573, PMID:23211528) using binding assays and functional rescue with domain mutants\",\n      \"pmids\": [\"22689573\", \"23211528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RNF4, a SUMO-targeted ubiquitin E3 ligase, synthesizes hybrid SUMO-ubiquitin chains at DSBs; RAP80 binds these hybrid chains through its SIM (nanomolar affinity) to promote BRCA1 recruitment; RNF4 depletion impairs RAP80 and BRCA1 foci formation.\",\n      \"method\": \"In vitro binding assays with hybrid SUMO-ubiquitin chains (affinity measurements), siRNA knockdown of RNF4 with foci readouts, co-immunoprecipitation\",\n      \"journal\": \"Science Signaling\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vitro affinity binding plus genetic knockdown with functional readout, demonstrates mechanistic connection between SUMO and ubiquitin pathways\",\n      \"pmids\": [\"23211528\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"NMR structure of the SUMO-2·phospho-RAP80 SIM complex shows that CK2-dependent phosphorylation of the RAP80 SIM enhances affinity and specificity for SUMO-2 via electrostatic interactions with the isoform-specific SIM recognition module of SUMO-2.\",\n      \"method\": \"NMR spectroscopy, NMR structure determination, phosphopeptide binding assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure with phosphorylation-dependent affinity measurements, single lab but rigorous structural approach\",\n      \"pmids\": [\"26719330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAP80 directly interacts with estrogen receptor alpha (ERα) in an agonist-dependent manner through the hinge/LBD of ERα; RAP80 UIMs reduce ERα polyubiquitination and increase ERα protein levels and transcriptional activity; UIM deletion abolishes these effects without affecting ERα binding.\",\n      \"method\": \"Mammalian two-hybrid, GST pull-down, co-immunoprecipitation, siRNA knockdown, reporter assays, ubiquitination assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal co-IP and GST pull-down combined with functional UIM deletion assays, single lab\",\n      \"pmids\": [\"17311814\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAP80 functions as an active transcriptional repressor and interacts with the retinoid-related testis-associated receptor (RTR) through its hinge domain; RAP80 competes with co-repressor N-CoR for RTR binding and inhibits RTR-N-CoR interaction.\",\n      \"method\": \"Mammalian two-hybrid, GST pull-down, co-immunoprecipitation, deletion/point mutation analysis, transcriptional reporter assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro pull-down plus co-IP plus functional transcriptional assays, single lab, single paper\",\n      \"pmids\": [\"12080054\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAP80 is a target of SUMO-1 and SUMO-3 modification in intact cells; the SUMO-conjugating enzyme UBC9 interacts with RAP80 through residues 122–204; UBC9 overexpression enhances RAP80 mono- and multi-sumoylation.\",\n      \"method\": \"Yeast two-hybrid screen, co-immunoprecipitation, GST pull-down, in vivo sumoylation assays\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP and in-cell sumoylation assays, single lab, multiple methods but no functional consequence established\",\n      \"pmids\": [\"17698038\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"ATM phosphorylates RAP80 at Ser205 in cells exposed to ionizing radiation within 5 minutes after irradiation; UV irradiation induces RAP80 Ser205 phosphorylation via ATR (not ATM); this phosphorylation is not required for IRIF formation.\",\n      \"method\": \"Phospho-specific antibody generation, ATM/ATR inhibitor treatment, immunofluorescence, kinase assays\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phospho-specific antibody validated with ATM inhibitors plus in vitro kinase assay (PMID:17621610 and 18519686), single lab\",\n      \"pmids\": [\"18519686\", \"17621610\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"RAP80 interacts with p53 and the E3 ubiquitin ligase HDM2 to promote HDM2-dependent p53 polyubiquitination; RAP80 is transcriptionally induced by p53 in a DNA-damage-responsive manner through a noncanonical p53 response element, forming an autoregulatory loop.\",\n      \"method\": \"Promoter analysis, co-immunoprecipitation, ubiquitination assays, siRNA knockdown with p53 target gene and apoptosis readouts\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP for protein interaction, in vivo ubiquitination assay, promoter reporter assay, functional siRNA knockdown; single lab\",\n      \"pmids\": [\"19433585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RAP80 protein levels fluctuate during the cell cycle; RAP80 is degraded by APC/C(Cdc20) during mitosis and APC/C(Cdh1) during G1 phase through a conserved destruction box (D-box); knockdown of Cdc20 or Cdh1 blocks RAP80 degradation; overexpression of a D-box deletion mutant attenuates mitotic progression.\",\n      \"method\": \"Cell cycle synchronization, flow cytometry, siRNA knockdown of Cdc20/Cdh1, ubiquitination assays, D-box mutant expression\",\n      \"journal\": \"Molecular Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — D-box mutagenesis, siRNA of specific E3 components, and functional mitotic progression readout; single lab\",\n      \"pmids\": [\"22426463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Cdk1-cyclin B1 complex phosphorylates RAP80 at Ser677; this phosphorylation occurs in M phase and is induced by ionizing radiation; Ser677Ala mutation sensitizes cells to IR and impairs G2/M checkpoint control.\",\n      \"method\": \"In vitro kinase assay, phosphopeptide-specific antibody, Ser677Ala mutant expression, IR sensitivity assays, G2/M checkpoint assays\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro kinase assay with phospho-specific antibody validation and functional mutant analysis; single lab\",\n      \"pmids\": [\"23264621\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"MDC1 directly binds RAP80 through its tandem BRCT domain and the UIMs of RAP80; this interaction depends on UBC13-dependent ubiquitylation of MDC1 at K1977; K1977 of MDC1 is required for RAP80 focus formation at DSBs.\",\n      \"method\": \"Co-immunoprecipitation, direct binding assay, UBC13 knockdown, MDC1 K1977 mutagenesis, foci assays\",\n      \"journal\": \"DNA Repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding demonstrated with domain mapping, ubiquitination-dependence shown by E2 knockdown and site mutagenesis; single lab\",\n      \"pmids\": [\"21622030\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RAP80 acts as a scaffold protein for the BRCA1-A complex; loss of RAP80 (in RAP80-null TOV-21G cells) disrupts the entire complex and suppresses recruitment of BRCA1, CCDC98, NBA1, BRCC36 and BRE to DSBs; reconstitution with wild-type RAP80 rescues these defects.\",\n      \"method\": \"RAP80-null cell line identification, co-immunoprecipitation, foci assays, reconstitution experiments, IR sensitivity assay\",\n      \"journal\": \"PloS ONE\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reconstitution in null cell line with multiple complex component readouts; single lab\",\n      \"pmids\": [\"22792303\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RAP80-deficient mice develop B-cell lymphomas with clonal chromosomal translocations and are hypersensitive to ionizing radiation; RAP80-null MEFs show impaired DSB repair due to loss of BRCA1-A complex recruitment to damage sites.\",\n      \"method\": \"RAP80 knockout mouse generation, tumor surveillance, IR sensitivity assays, γH2AX/foci assays in MEFs\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — germline knockout with multiple in vivo and cellular phenotypic readouts; corroborated by independent RAP80-null mouse study (PMID:22896338)\",\n      \"pmids\": [\"22539352\", \"22896338\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"USP26 and USP37 are recruited to DSBs where they remove RNF168-induced ubiquitin conjugates, limiting RAP80-BRCA1 spreading from DSBs; their depletion impairs HR, and this defect is rescued by simultaneous RAP80 depletion, placing USP26/USP37 as antagonists of RAP80-mediated BRCA1 sequestration.\",\n      \"method\": \"Genetic screen, siRNA knockdown epistasis (single and double depletions), foci assays, HR reporter assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis (double depletion rescue) combined with foci and HR functional readouts; single lab\",\n      \"pmids\": [\"26101254\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"TIP60-mediated H4K16 acetylation prevents 53BP1 binding to H4K20me2; Fanconi anemia pathway inactivation impairs FANCD2 monoubiquitination and TIP60 relocalization, leading to aberrant chromatin accumulation of RAP80 and 53BP1 that impairs resection and HR.\",\n      \"method\": \"siRNA knockdown, ChIP, histone modification analysis, HR assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pathway epistasis through siRNA and chromatin assays; single lab; RAP80 is one of several readouts\",\n      \"pmids\": [\"26446986\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"TRAIP/RNF206 is a novel RAP80-interacting protein that acts upstream of RAP80; TRAIP depletion impairs RAP80 and BRCA1 accumulation at DNA lesions; TRAIP localizes to damage sites through direct interaction with RNF20-RNF40 via its C-terminus, while its N-terminus mediates RAP80 binding.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown with foci readouts, domain mapping, in vitro binding assays\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — Co-IP with domain mapping, siRNA epistasis showing TRAIP upstream of RAP80; single lab\",\n      \"pmids\": [\"26781088\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"USP13 is phosphorylated by ATM following DNA damage and deubiquitinates RAP80, promoting RAP80 recruitment to DSBs and proper DDR; USP13 depletion or inhibition sensitizes ovarian cancer cells to cisplatin and PARP inhibitors.\",\n      \"method\": \"Co-immunoprecipitation, in vitro deubiquitination assays, ATM inhibitor treatment, siRNA knockdown, foci assays, drug sensitivity assays\",\n      \"journal\": \"Nature Communications\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro DUB assay and Co-IP with ATM-dependent phosphorylation and functional drug sensitivity readout; single lab\",\n      \"pmids\": [\"28569838\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The inter-UIM linker length of RAP80 is a critical determinant of K63-linked polyubiquitin binding affinity; modifying linker length by insertion or deletion changes binding affinity and impairs translocation to DSBs.\",\n      \"method\": \"In vitro GST pull-down assays with linker mutants, foci assays\",\n      \"journal\": \"BMB Reports\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, in vitro pull-down only; consistent with structural data but no in vivo mechanistic follow-up\",\n      \"pmids\": [\"19944020\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"The RAP80 ΔE81 deletion mutant (c.241-243delGAA) found in familial breast cancer cases displays significantly reduced ubiquitin binding and DSB localization, impairs BRCA1 and Abraxas DSB recruitment, and increases chromosomal aberrations.\",\n      \"method\": \"Ubiquitin binding assays, foci formation assays, chromosomal aberration analysis, expression of ΔE81 allele\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — functional domain mutation with multiple readouts (ubiquitin binding, foci, chromosomal aberrations); single lab; mechanism confirmed by structural studies (PMID:24627472)\",\n      \"pmids\": [\"19305427\", \"24627472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"NMR spectroscopy shows that the ΔE81 deletion causes a structural frameshift in the N-cap of the first UIM alpha-helix, abolishing multivalent polyubiquitin binding by disrupting favorable electrostatic interactions between UIM1 and ubiquitin.\",\n      \"method\": \"NMR spectroscopy, structural comparison of wild-type and ΔE81 UIM1\",\n      \"journal\": \"The Journal of Biological Chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structural determination with mechanistic explanation of binding loss; single lab but rigorous structural approach\",\n      \"pmids\": [\"24627472\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"BRCA1 PARsylation and RAP80-bound BRCA1 together regulate normal interaction of BRCA1 with CtIP and BACH1 in nuclear foci; simultaneous loss of RAP80 and failure of BRCA1 PARsylation results in dysregulated accumulation of BRCA1 complexes in foci, hyper-recombination, and gross chromosomal disorder.\",\n      \"method\": \"Genetic depletion (siRNA/knockout), PARP inhibition, HR assays, foci kinetics, chromosomal instability measurement\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — double loss-of-function genetic analysis with multiple readouts; single lab\",\n      \"pmids\": [\"31932421\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"FANCG undergoes K63-linked polyubiquitination in response to DNA damage, which is required for its interaction with the RAP80-BRCA1 complex and subsequent HR repair of ICLs; BRCC36 deubiquitinates K63-ubiquitinated FANCG in vitro and in vivo.\",\n      \"method\": \"Co-immunoprecipitation, in vitro ubiquitination/deubiquitination assays, FANCG 3KR mutant expressing cells, HR reporter assays\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro deubiquitination assay plus Co-IP with functional mutant analysis; single lab\",\n      \"pmids\": [\"25132264\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RAP80 binds the mitochondrial protein p32 through its arginine-rich C-terminal domain; a subset of RAP80 localizes to mitochondria; RAP80 deficiency reduces p32 protein levels and p32-dependent mitochondrial proteins (Rieske, COX1), reducing mitochondrial membrane potential and oxygen consumption.\",\n      \"method\": \"Yeast two-hybrid screening, co-immunoprecipitation, subcellular fractionation/mitochondrial localization, siRNA knockdown with mitochondrial function readouts\",\n      \"journal\": \"Biochemical and Biophysical Research Communications\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single lab, Co-IP plus fractionation without rigorous mechanistic follow-up; novel localization claim with limited supporting data\",\n      \"pmids\": [\"28842250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAP80 prevents CtIP-mediated nucleolytic processing of ssDNA in R-loops near DSBs, thereby promoting efficient DSB repair via transcription-associated end joining dependent on BRCA1, Polθ, and LIG1/3; RAP80 depletion increases chromosome translocations and deletions due to unscheduled R-loop ssDNA processing.\",\n      \"method\": \"siRNA knockdown, R-loop detection (S9.6 immunofluorescence), CtIP epistasis, chromosomal translocation and deletion assays\",\n      \"journal\": \"Cell Reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis (double depletion of RAP80 and CtIP), R-loop detection, and chromosomal instability readouts; single lab\",\n      \"pmids\": [\"35108530\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"RAP80 undergoes liquid-liquid phase separation (LLPS) at DSBs through an intrinsically disordered region (IDR) at its N-terminus; K63-linked polyubiquitin chains at DSBs strongly enhance RAP80 phase separation; abolishing RAP80 condensation suppresses BRCA1 foci formation and increases radiosensitivity.\",\n      \"method\": \"In vitro phase separation assays, cellular condensate imaging, IDR deletion mutants, radiosensitivity assays\",\n      \"journal\": \"Nucleic Acids Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and cellular LLPS assays with IDR mutants and functional readout; single lab\",\n      \"pmids\": [\"37638744\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"DOT1L methyltransferase is recruited to chromatin after DNA damage and methylates RAP80 at multiple lysines; methylated RAP80 binds ubiquitinated H2A and triggers BRCA1-A complex recruitment to DSBs; DOT1L inhibition or mutation of RAP80 methylation sites reduces BRCA1 recruitment and enhances radiosensitivity.\",\n      \"method\": \"In vitro methylation assays, methylation site identification by MS, Co-IP, ChIP, ubiquitinated H2A pull-down, siRNA/inhibitor knockdown with foci and radiosensitivity readouts\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro methylation assay plus functional Co-IP and pull-down showing methylation-dependent H2A binding; single lab\",\n      \"pmids\": [\"39172790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"RAP80 performs a BRCA1-independent repair function specific to topoisomerase II inhibitor (etoposide) damage; RAP80-null DT40 cells are proficient in HR and NHEJ but sensitive to etoposide; RAP80/BRCA1 double knockout cells are more sensitive to etoposide than BRCA1 single knockouts.\",\n      \"method\": \"Genetic disruption of RAP80 in DT40 cells, single and double mutant analysis, drug sensitivity assays (etoposide, other agents), HR and NHEJ assays\",\n      \"journal\": \"Cancer Research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic KO with epistasis (double mutant more sensitive), multiple DNA damage agent readouts; single lab\",\n      \"pmids\": [\"20959489\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"SENP3 deSUMOylates RAP80 to facilitate timely RAP80 dissociation from DSB sites during later stages of repair; SENP3 depletion causes aberrant prolonged RAP80 SUMOylation and retention at damage foci, impairing HR repair progression.\",\n      \"method\": \"Co-immunoprecipitation, in vivo SUMOylation assays, siRNA knockdown of SENP3, foci assays, HR and IR sensitivity assays\",\n      \"journal\": \"Acta Biochimica et Biophysica Sinica\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single recent paper, Co-IP and in-vivo sumoylation assays, no structural or in vitro reconstitution data; functional consequence plausible but single lab single method\",\n      \"pmids\": [\"42093510\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAP80 (UIMC1) is a multivalent ubiquitin/SUMO receptor that forms the core of the BRCA1-A complex: its tandem UIMs bind K63-linked polyubiquitin chains generated by the RNF8-Ubc13 cascade at DSBs (with selectivity arising from linkage-specific avidity enforced by the inter-UIM helical linker), while an upstream SIM binds SUMO-2/3 and hybrid SUMO-ubiquitin chains synthesized by RNF4, together recruiting the Abraxas–BRCC36–MERIT40–BRCA1–BARD1 complex to break sites; paradoxically, rather than solely promoting homologous recombination, the RAP80-BRCA1 complex actively suppresses excessive HR by restraining CtIP-dependent end resection and sequestering BRCA1 away from PALB2-BRCA2-RAD51, thereby tuning the balance between competing repair pathways; RAP80 undergoes multiple post-translational modifications (ATM/ATR phosphorylation at Ser205, Cdk1 phosphorylation at Ser677, CK2 phosphorylation of the SIM, K63-ubiquitination reversed by USP13, SUMOylation reversed by SENP3, DOT1L-mediated methylation enabling H2AX binding, and APC/C-dependent proteasomal degradation during mitosis/G1) that collectively regulate its activity and abundance throughout the cell cycle, while its intrinsically disordered region drives phase separation at DSBs to concentrate BRCA1 recruitment.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAP80 (UIMC1) is a multivalent ubiquitin/SUMO receptor that nucleates the BRCA1-A complex at DNA double-strand breaks (DSBs) and governs the magnitude of the DNA damage response [#0, #21]. Its tandem ubiquitin-interacting motifs (UIMs) selectively recognize K63-linked polyubiquitin chains generated by the RNF8-Ubc13 cascade, with linkage specificity arising from an inter-UIM helical linker that positions the two UIMs to simultaneously engage the proximal and distal ubiquitin moieties of K63 di-ubiquitin [#2, #3, #6]. A complementary SUMO-interacting motif (SIM) binds SUMO-2/3 and the hybrid SUMO-ubiquitin chains synthesized by RNF4, and CK2-dependent phosphorylation of the SIM enhances its affinity for SUMO-2; both SIM and UIM modules are required for efficient RAP80 recruitment to breaks [#10, #11, #12]. Through an Abraxas-interacting region, RAP80 assembles and stabilizes the Abraxas-BRCC36-MERIT40-BRCA1-BARD1 complex, in which the BRCC36 deubiquitinase counterbalances RNF8-Ubc13 ubiquitination to set a steady-state ubiquitin level at breaks [#0, #4, #5, #21]. Functionally, the RAP80-BRCA1 complex restrains rather than simply promotes repair: it limits Mre11-CtIP-dependent end resection and suppresses excessive homologous recombination, and its loss causes hyper-resection, elevated HR, and chromosomal instability [#7, #8]. RAP80 activity and abundance are tuned across the cell cycle by ATM/ATR phosphorylation at Ser205, Cdk1 phosphorylation at Ser677, USP13-reversed ubiquitination, DOT1L-mediated methylation that enables binding to ubiquitinated H2A, and APC/C-dependent destruction-box proteolysis in mitosis and G1 [#16, #18, #19, #26, #35]. Its N-terminal intrinsically disordered region drives K63-polyubiquitin-stimulated liquid-liquid phase separation that concentrates BRCA1 recruitment at breaks [#34]. RAP80 is a tumor suppressor in vivo, as RAP80-deficient mice develop B-cell lymphomas with clonal translocations, and a familial breast-cancer ΔE81 allele disrupts UIM1 structure and ubiquitin binding to impair complex recruitment [#22, #28, #29].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established RAP80 as the ubiquitin sensor that links K63-polyubiquitin at breaks to BRCA1 recruitment, defining the BRCA1-A complex and its checkpoint/repair role.\",\n      \"evidence\": \"Phosphopeptide affinity proteomics, reciprocal Co-IP, UIM mutagenesis, and IR-induced foci/checkpoint assays across three simultaneous papers\",\n      \"pmids\": [\"17525340\", \"17525341\", \"17525342\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of K63 selectivity\", \"Upstream E3/E2 generating the chains not yet defined here\"]\n    },\n    {\n      \"year\": 2007,\n      \"claim\": \"Identified the upstream RNF8-Ubc13 cascade and the Abraxas-interacting region, placing RAP80 downstream of MDC1-γH2AX-dependent ubiquitination.\",\n      \"evidence\": \"siRNA epistasis of Ubc13/RNF8, domain mapping, and foci assays\",\n      \"pmids\": [\"18077395\", \"17525341\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address how RAP80 modulates resection or HR outcome\", \"Stoichiometry of complex assembly unresolved\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the structural mechanism of K63 linkage selectivity through tandem-UIM avidity enforced by the inter-UIM helical linker.\",\n      \"evidence\": \"2.2 Å crystal structure and NMR of tandem UIMs bound to K63 di-ubiquitin with linker-length mutants\",\n      \"pmids\": [\"19328070\", \"19536136\", \"22350954\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address SUMO-chain recognition\", \"In vivo consequence of altered linker only partially tested\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Showed RAP80 builds a DUB-active complex with BRCC36 and MERIT40 that antagonizes RNF8-Ubc13 ubiquitination, balancing ubiquitin levels at breaks.\",\n      \"evidence\": \"Catalytically inactive BRCC36 mutants, RNF8/BRCC36 epistasis, and complex-component knockdowns with foci/DUB readouts\",\n      \"pmids\": [\"19202061\", \"19261746\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Physiological substrates of the DUB at breaks incompletely defined\", \"Quantitative balance point not measured\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Reframed RAP80-BRCA1 as a restraint on repair, showing it limits CtIP-Mre11 end resection and suppresses excessive HR to preserve genome stability.\",\n      \"evidence\": \"RAP80/BRCC36 knockdown with HR reporters, RPA/ssDNA resection assays, foci kinetics, and chromosomal instability measurements\",\n      \"pmids\": [\"21406551\", \"21335604\", \"21622030\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which complex blocks resection not fully defined\", \"Relationship to BRCA1 partitioning toward PALB2-BRCA2 not directly tested here\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Added a SUMO arm: a SIM binds SUMO-2/3 and RNF4-made hybrid SUMO-ubiquitin chains, and both SIM and UIMs are needed for recruitment, integrating SUMO and ubiquitin signaling.\",\n      \"evidence\": \"In vitro affinity binding to hybrid chains, RNF4 knockdown, and SIM/UIM rescue foci assays\",\n      \"pmids\": [\"22689573\", \"23211528\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relative contribution of SUMO vs ubiquitin reading in vivo unquantified\", \"Identity of the SUMOylated substrates at breaks unclear\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Established cell-cycle control of RAP80 abundance and activity via APC/C destruction-box proteolysis and Cdk1 Ser677 phosphorylation.\",\n      \"evidence\": \"Synchronization, Cdc20/Cdh1 knockdown, D-box mutants, in vitro Cdk1 kinase assays, and G2/M checkpoint readouts\",\n      \"pmids\": [\"22426463\", \"23264621\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interplay between degradation and modification not integrated\", \"Functional impact of fluctuation on repair timing not directly tested\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Confirmed RAP80 as the scaffold whose loss collapses BRCA1-A complex recruitment, validated in a RAP80-null human line by reconstitution.\",\n      \"evidence\": \"RAP80-null TOV-21G cells, Co-IP, foci of complex components, and wild-type rescue\",\n      \"pmids\": [\"22792303\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single cell-line context\", \"Quantitative scaffolding contributions of individual subunits unresolved\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Demonstrated RAP80 is a tumor suppressor in vivo, with knockout mice developing lymphomas and IR hypersensitivity from defective complex recruitment.\",\n      \"evidence\": \"Germline knockout mice, tumor surveillance, IR sensitivity, and γH2AX/foci assays in MEFs, corroborated by an independent knockout\",\n      \"pmids\": [\"22539352\", \"22896338\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Tissue specificity of tumor predisposition not mechanistically explained\", \"Contribution of HR suppression vs other functions to tumorigenesis unresolved\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Provided the structural explanation for a familial breast-cancer allele, showing ΔE81 frameshifts the UIM1 N-cap and abolishes multivalent ubiquitin binding.\",\n      \"evidence\": \"NMR comparison of wild-type and ΔE81 UIM1 with ubiquitin-binding and foci assays\",\n      \"pmids\": [\"24627472\", \"19305427\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Disease causality at the population level not established by structure alone\", \"Penetrance and modifier effects unaddressed\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Defined antagonistic DUBs (USP26/USP37) that limit RAP80-BRCA1 spreading, and CK2 phosphorylation enhancing SIM-SUMO-2 specificity.\",\n      \"evidence\": \"Genetic screen with double-depletion rescue, foci/HR assays, and NMR of SUMO-2·phospho-SIM complex\",\n      \"pmids\": [\"26101254\", \"26719330\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Coordination of these regulators in vivo not integrated\", \"Temporal sequence of phospho-SIM activation during repair unclear\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified USP13 as an ATM-activated DUB that deubiquitinates RAP80 to promote its recruitment, with therapeutic relevance to PARP/cisplatin sensitivity.\",\n      \"evidence\": \"In vitro DUB assays, ATM-dependent phosphorylation, Co-IP, foci, and drug sensitivity assays\",\n      \"pmids\": [\"28569838\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Specific RAP80 ubiquitination sites reversed by USP13 not mapped\", \"Single lab\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Extended RAP80 function to R-loop protection, preventing CtIP processing of R-loop ssDNA near breaks to enable transcription-associated end joining.\",\n      \"evidence\": \"siRNA knockdown, S9.6 R-loop imaging, CtIP epistasis, and translocation/deletion assays\",\n      \"pmids\": [\"35108530\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Direct RAP80 binding to R-loop structures not shown\", \"Mechanism of CtIP restriction at R-loops unresolved\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Showed RAP80 IDR-driven, K63-polyubiquitin-stimulated phase separation concentrates BRCA1 recruitment at breaks.\",\n      \"evidence\": \"In vitro phase separation, cellular condensate imaging, IDR deletion mutants, and radiosensitivity assays\",\n      \"pmids\": [\"37638744\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"In vivo necessity of condensation distinct from binding not fully separated\", \"Single lab\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Added a methylation layer: DOT1L methylates RAP80 to enable binding of ubiquitinated H2A and BRCA1-A recruitment.\",\n      \"evidence\": \"In vitro methylation, MS site mapping, ubiquitinated-H2A pull-down, ChIP, and foci/radiosensitivity assays\",\n      \"pmids\": [\"39172790\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interplay of methylation with UIM/SIM reading not integrated\", \"Single lab\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RAP80's multiple, partly redundant recruitment modes (UIM, SIM, methyl-H2A reading, phase separation) and its many post-translational modifications are quantitatively coordinated in time to switch BRCA1-A from HR restraint to other repair functions remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified kinetic model integrating modifications and recruitment modes\", \"Relative contributions of SUMO vs ubiquitin vs methylation reading not partitioned in vivo\", \"Mechanism linking HR restraint to alternative end-joining/R-loop functions unclear\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [0, 21]},\n      {\"term_id\": \"GO:0140110\", \"supporting_discovery_ids\": [14]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [0, 34]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 2, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [18, 19]},\n      {\"term_id\": \"R-HSA-392499\", \"supporting_discovery_ids\": [4, 11, 26]}\n    ],\n    \"complexes\": [\n      \"BRCA1-A complex\",\n      \"BRCC36 deubiquitinase complex\"\n    ],\n    \"partners\": [\n      \"ABRAXAS1\",\n      \"BRCC36\",\n      \"BRCA1\",\n      \"BABAM1\",\n      \"MDC1\",\n      \"RNF4\",\n      \"USP13\",\n      \"TRAIP\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":8,"faith_total":8,"faith_pct":100.0}}