{"gene":"RPA2","run_date":"2026-06-10T06:43:37","timeline":{"discoveries":[{"year":2006,"finding":"ATR directly phosphorylates RPA2 on chromatin at Thr21 and Ser33 in response to UV-induced replication fork stalling, and phospho-mimetic mutations at these ATR-dependent sites impair RPA2 association with replication centers, mechanistically linking ATR phosphorylation of RPA2 to inhibition of DNA replication in S-phase.","method":"Phospho-site mutagenesis (T21A, S33A and phospho-mimetic alleles), chromatin fractionation, DNA synthesis assays, ATR-dependent kinase assays in human cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — site-directed mutagenesis with functional readout (DNA synthesis inhibition, replication center association), multiple orthogonal approaches in a single focused study","pmids":["17035231"],"is_preprint":false},{"year":2010,"finding":"Protein phosphatase 4 (PP4), via its regulatory subunit PP4R2, dephosphorylates RPA2 in vitro and in cells; PP4R2 mediates a DNA damage-dependent physical association between RPA2 and the PP4C catalytic subunit. PP4-mediated dephosphorylation of RPA2 is required for RAD51 loading and efficient homologous recombination (HR) after DSBs.","method":"In vitro phosphatase assay with purified PP4 and phospho-RPA2, siRNA knockdown of PP4R2, co-immunoprecipitation, RAD51 foci assay, HR reporter assay","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1–2 / Moderate — in vitro dephosphorylation assay plus reciprocal Co-IP plus functional HR assay, multiple orthogonal methods in one study","pmids":["20154705"],"is_preprint":false},{"year":2001,"finding":"The RPA2 subunit contains OB-fold DNA-binding domain D (DBD-D) which engages ssDNA substrates of ≥23–27 nucleotides; inactivation of DBD-D by mutation of conserved aromatic stacking residues has little effect on short substrates but abolishes RPA contact with oligonucleotides ≥27 nt, supporting a sequential binding model where DBD-D extends the footprint on longer ssDNA.","method":"In vitro ssDNA binding assays with purified recombinant yeast RPA carrying single-DBD inactivating mutations, protein-DNA crosslinking","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro binding with mutagenesis and crosslinking, multiple substrates tested; single lab but rigorous biochemistry","pmids":["11479296"],"is_preprint":false},{"year":2010,"finding":"RPA2 hyperphosphorylation (induced by hydroxyurea-mediated replication arrest) promotes association of RPA2 with ssDNA and RAD51, is required for RAD51 recruitment and HR-mediated repair of HU-induced damage, and its loss leads to chromosomal aberrations and reduced viability specifically under replication stress but not after ionizing radiation.","method":"Phosphorylation-deficient RPA2 mutant expression, co-immunoprecipitation with RAD51, HR reporter assays, immunofluorescence for RAD51 foci, clonogenic survival","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean mutant rescue with multiple functional readouts (HR, foci, survival), single lab","pmids":["20130019"],"is_preprint":false},{"year":2011,"finding":"DNA-PK phosphorylates RPA2 at Ser4 and Ser8 primarily in response to DSBs; this hyperphosphorylation suppresses unscheduled homologous recombination (evidenced by increased RAD51 foci and HR in S4A/S8A mutant cells) and delays mitotic entry, allowing proper DSB repair.","method":"S4A/S8A phospho-mutant RPA2 expression, DNA-PK inhibitors, RAD51 foci quantification, HR reporter assay, cell cycle analysis","journal":"PloS one","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — phospho-mutant cells with pharmacological inhibitor confirmation, multiple readouts, single lab","pmids":["21731742"],"is_preprint":false},{"year":2008,"finding":"RPA2 phosphorylation (phosphorylated or phosphomimetic RPA) weakens the direct physical interaction between RPA and the MRN complex (MRE11, RAD50, NBS1), and the N-terminal OB-fold of RPA1 (requiring Arg31 and Arg41) is the critical determinant of the RPA–MRN protein–protein interaction.","method":"Pulldown assays with purified proteins, co-immunoprecipitation, RPA1 N-terminal deletion and point mutants (R31A, R41A), phosphomimetic RPA2 substitution","journal":"Biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct protein-protein interaction with purified components plus mutagenesis, single lab","pmids":["19586055"],"is_preprint":false},{"year":2008,"finding":"In DNA polymerase eta-deficient cells, cisplatin- and oxaliplatin-induced hyperphosphorylation of RPA2 at Ser4/Ser8 is mediated by DNA-PK (blocked by NU7441) rather than ATM; ATR is required for initial RPA2 recruitment to chromatin and subsequently enables DNA-PK-mediated Ser4/Ser8 phosphorylation.","method":"Selective kinase inhibitors (NU7441 for DNA-PK, KU-55933 for ATM, CGK733 for ATM/ATR), immunofluorescence, subcellular fractionation, phospho-specific antibodies","journal":"DNA repair","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — pharmacological dissection of kinase contributions with fractionation confirmation, single lab","pmids":["18289945"],"is_preprint":false},{"year":2005,"finding":"53BP1 physically associates with RPA1 and RPA2 (interaction disrupted by camptothecin-induced DNA damage), and dominant-negative 53BP1 fragments or 53BP1 siRNA knockdown inhibit camptothecin-induced RPA2 hyperphosphorylation, placing 53BP1 upstream of RPA2 phosphorylation in the DNA damage response.","method":"Co-immunoprecipitation followed by tandem MS identification, immunoblotting, dominant-negative 53BP1 stable cell lines, siRNA knockdown, RPA2 phosphorylation assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — reciprocal Co-IP with MS confirmation plus genetic (DN and siRNA) functional follow-up; single lab","pmids":["15856006"],"is_preprint":false},{"year":2013,"finding":"RPA2 translation is regulated via an internal ribosome entry site (IRES) located −50 to −150 bases upstream of the start codon; eIF3a directly binds this IRES element and suppresses RPA2 synthesis, providing a translational control mechanism for RPA2 expression during DNA damage response.","method":"IRES reporter assays, eIF3a RNA binding (EMSA/pulldown), siRNA knockdown of eIF3a, polysome profiling, DNA damage treatment","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct RNA-protein binding assay plus functional IRES reporter, single lab, two methods","pmids":["23393223"],"is_preprint":false},{"year":2019,"finding":"HERC2 E3 ubiquitin ligase interacts with RPA2 via its C-terminal HECT domain and mediates ubiquitination-dependent degradation of ATR-phosphorylated RPA2 (Ser33); HERC2 depletion inhibits ATR-mediated Ser33 phosphorylation under low-level replication stress, while loss of HERC2 catalytic activity causes constitutively elevated Ser33-phospho-RPA2. HERC2 E3 activity is epistatic to RPA in suppression of G-quadruplex DNA structures.","method":"Co-immunoprecipitation, siRNA knockdown and rescue with HERC2 C-terminal fragment, phospho-specific immunoblotting, ATR inhibitor treatment, siRNA epistasis for G4 suppression","journal":"Scientific reports","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus rescue experiment plus epistasis analysis plus pharmacological inhibitor, single lab","pmids":["31582797"],"is_preprint":false},{"year":2021,"finding":"The flexible winged-helix (WH) domain of RPA2 directly interacts with the N-terminal RPA-binding helix of UNG2 (uracil-DNA glycosylase), enabling efficient excision of uracil from RPA-coated ssDNA; this interaction is promoted by mono-ubiquitination of UNG and diminished by cell-cycle-regulated phosphorylations on UNG. Six additional DNA repair/replication fork remodeling proteins also bind the RPA2-WH domain.","method":"In vitro uracil excision assays on RPA-coated ssDNA, binding/interaction assays with WH domain mutants, NMR/structural analysis of interaction, ubiquitination and phosphorylation of UNG modulating the interaction","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — in vitro reconstituted activity assay plus mutagenesis of WH domain plus identification of binding helix in UNG, multiple methods in single study","pmids":["33784377"],"is_preprint":false},{"year":2017,"finding":"RPA2 physically interacts with menin (the MEN1 tumor suppressor protein); ectopic RPA2 expression disrupts the menin–NF-κB p65 complex, relieving menin's inhibitory effect on NF-κB-regulated transcription and promoting oncogenic gene expression. Conversely, RPA2 knockdown enhances the menin–p65 complex and suppresses NF-κB target genes.","method":"Co-immunoprecipitation/binding assays, RPA2 overexpression and siRNA knockdown, NF-κB reporter assay, immunoblotting for NF-κB targets","journal":"Carcinogenesis","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — Co-IP plus functional reporter assay plus bidirectional manipulation (OE and KD), single lab","pmids":["28007956"],"is_preprint":false},{"year":2024,"finding":"A heterozygous Y256C variant in RPA2 reduces RPA2 affinity for RFWD3 (ubiquitin ligase) and reduces RPA ubiquitination, causing accumulation of RPA at telomeres without triggering ATR activation, resulting in short and dysfunctional telomeres and telomere biology disorder in patients.","method":"Knock-in cell lines engineered with Y256C mutation, telomere length measurement, RPA telomere localization (ChIP/IF), ATR activation assays, RPA–RFWD3 interaction assays, ubiquitination assays","journal":"Genes & development","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — engineered knock-in cells with multiple functional readouts (telomere length, RPA foci, ATR signaling, ubiquitination), single study","pmids":["39231615"],"is_preprint":false},{"year":2024,"finding":"O-GlcNAcylation of RPA2 by OGT occurs at Ser4/Ser8 (mapped by mass spectrometry) and directly antagonizes phosphorylation at these sites; OGT interacts with RPA2 and this association is reduced by etoposide treatment. Ser4/Ser8 O-GlcNAcylation impairs downstream Chk1 activation and promotes inappropriate cell cycle progression, indicating a checkpoint defect.","method":"HCD mass spectrometry mapping of O-GlcNAc sites, OGT co-immunoprecipitation, phospho-specific and O-GlcNAc-specific immunoblotting, etoposide treatment, Chk1 activation assay, cell cycle analysis","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 1–2 / Moderate — MS-based site mapping plus Co-IP plus functional checkpoint assay, single lab, multiple methods","pmids":["39491647"],"is_preprint":false},{"year":2025,"finding":"TRIM21 mediates K63-linked ubiquitination of RPA2 under basal conditions; upon DNA damage, ATR phosphorylates TRIM21 at Ser41, causing dissociation of the TRIM21–RPA2 complex and a shift from K63- to K6-linked ubiquitination of RPA2. K6-linked ubiquitination stabilizes the RPA2–ATRIP complex and is required for efficient homologous recombination repair.","method":"Co-immunoprecipitation, ubiquitination linkage-specific assays, TRIM21 S41 phospho-mutant expression, siRNA knockdown, HR repair reporter assay, ATR kinase assay","journal":"Oncogene","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP plus ubiquitin linkage assays plus HR reporter, single lab, multiple methods","pmids":["39900724"],"is_preprint":false},{"year":2025,"finding":"TTK kinase directly interacts with RPA2 and phosphorylates RPA2 at Ser33, which activates the ATR signaling pathway and promotes homologous recombination-mediated repair, contributing to PARP inhibitor resistance in ovarian cancer cells.","method":"Co-immunoprecipitation of TTK–RPA2, phospho-Ser33 immunoblotting, TTK knockdown and inhibitor treatment, ATR pathway activation assays, in vitro and in vivo HR assays","journal":"Communications biology","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — direct physical interaction plus phosphorylation site-specific readout plus in vivo model confirmation, single lab","pmids":["40617868"],"is_preprint":false},{"year":2025,"finding":"CSDE1 forms a ternary complex with eIF3a protein and RPA2 mRNA (confirmed by biotin pulldown, EMSA and co-IP), upregulating RPA2 translation; this CSDE1-eIF3a-RPA2 regulatory axis enhances nucleotide excision repair and homologous recombination and suppresses cGAS-STING signaling, conferring genotoxic drug resistance.","method":"Biotin-RNA pulldown, EMSA, co-immunoprecipitation, CSDE1 knockout mouse models, DNA damage reporter assays","journal":"Drug resistance updates","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct RNA-protein binding demonstrated by three orthogonal methods plus in vivo knockout validation, single lab","pmids":["40398074"],"is_preprint":false},{"year":2024,"finding":"AXL receptor tyrosine kinase physically interacts with RPA2, promotes its recruitment to DNA damage sites, and tyrosinates RPA2 at Tyr9, which in turn promotes CHK1 phosphorylation and strengthens HR repair capacity in hepatocellular carcinoma cells.","method":"Co-immunoprecipitation of AXL–RPA2, phospho-specific immunoblotting, AXL kinase inhibitor (bemcentinib), siRNA knockdown, HR efficiency assay","journal":"Heliyon","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single Co-IP plus inhibitor data, tyrosination site not validated by mutagenesis, single lab","pmids":["39281567"],"is_preprint":false}],"current_model":"RPA2 (the 32 kDa middle subunit of the heterotrimeric RPA complex) binds ssDNA through its OB-fold domain D to extend RPA's footprint on substrates >23 nt and interacts with repair/replication proteins via its winged-helix domain; its N-terminal tail is extensively phosphorylated by ATR (Thr21, Ser33), DNA-PK (Ser4, Ser8), and TTK (Ser33), with phosphorylation coordinating inhibition of replication initiation, regulation of RPA–MRN interactions, control of RAD51 loading and HR fidelity, and telomere maintenance, while counterbalancing modifications including PP4-mediated dephosphorylation, HERC2- and TRIM21-mediated ubiquitination (K63 vs. K6 linkage switch), and OGT-mediated O-GlcNAcylation at Ser4/Ser8 collectively fine-tune checkpoint activation, HR efficiency, and genome stability."},"narrative":{"mechanistic_narrative":"RPA2 is the middle subunit of the heterotrimeric single-stranded DNA-binding protein RPA, contributing an OB-fold DNA-binding domain (DBD-D) that extends the RPA footprint onto ssDNA substrates longer than ~23 nucleotides [PMID:11479296] and a flexible winged-helix (WH) domain that serves as a docking platform for repair and replication-fork enzymes, including UNG2, whose RPA-binding helix engages the WH domain to enable uracil excision from RPA-coated ssDNA [PMID:33784377]. The dominant mechanistic theme is regulation of the DNA damage response through the heavily modified RPA2 N-terminal tail: ATR phosphorylates Thr21/Ser33 upon replication fork stalling to inhibit replication initiation [PMID:17035231], DNA-PK phosphorylates Ser4/Ser8 to suppress untimely homologous recombination and delay mitotic entry [PMID:21731742], and these events are dynamically reversed by PP4-mediated dephosphorylation, which is itself required for RAD51 loading and efficient HR [PMID:20154705]. RPA2 phosphorylation status gates protein interactions central to repair-pathway choice, weakening the RPA–MRN association [PMID:19586055] while promoting RPA2 binding to RAD51 to drive HR under replication stress [PMID:20130019]. Beyond phosphorylation, RPA2 function is tuned by a switchable ubiquitin code—TRIM21-mediated K63 linkage under basal conditions converting to K6 linkage after ATR signaling to stabilize the RPA2–ATRIP complex and support HR [PMID:39900724]—and by O-GlcNAcylation at Ser4/Ser8 that antagonizes phosphorylation and impairs Chk1 checkpoint activation [PMID:39491647]. A heterozygous RPA2 Y256C variant that weakens RFWD3 binding and reduces RPA ubiquitination causes telomeric RPA accumulation, short dysfunctional telomeres, and a telomere biology disorder [PMID:39231615].","teleology":[{"year":2001,"claim":"Established the biochemical contribution of the RPA2 subunit to substrate engagement, showing its OB-fold extends RPA's grip onto longer ssDNA.","evidence":"In vitro ssDNA binding and crosslinking with purified RPA carrying single-DBD inactivating mutations","pmids":["11479296"],"confidence":"High","gaps":["Performed with yeast RPA; human-specific quantitative parameters not addressed","Does not connect DBD-D occupancy to downstream repair outcomes"]},{"year":2005,"claim":"Placed 53BP1 upstream of RPA2 hyperphosphorylation, defining an early signaling input to the RPA2 modification cascade.","evidence":"Co-IP/MS, dominant-negative and siRNA knockdown of 53BP1, RPA2 phosphorylation assay after camptothecin","pmids":["15856006"],"confidence":"Medium","gaps":["Did not identify the responsible kinase downstream of 53BP1","Direct vs. indirect basis of the interaction not resolved"]},{"year":2006,"claim":"Identified ATR as a direct RPA2 kinase at Thr21/Ser33 and linked this modification to inhibition of replication during fork stalling.","evidence":"Phospho-site and phospho-mimetic mutagenesis, chromatin fractionation, DNA synthesis assays in human cells","pmids":["17035231"],"confidence":"High","gaps":["Molecular mechanism by which phospho-RPA2 dissociates from replication centers not defined","Interplay with other tail sites not addressed"]},{"year":2008,"claim":"Showed RPA2 phosphorylation acts as a switch that weakens the RPA–MRN interaction, and mapped the interaction determinant to the RPA1 N-terminal OB-fold.","evidence":"Pulldowns/Co-IP with purified proteins, RPA1 deletion and R31A/R41A mutants, phosphomimetic RPA2","pmids":["19586055"],"confidence":"Medium","gaps":["Cellular consequence of MRN release for resection kinetics not directly measured","Which physiological kinase drives this in vivo not established here"]},{"year":2008,"claim":"Dissected the kinase hierarchy showing ATR enables initial chromatin recruitment that licenses DNA-PK-mediated Ser4/Ser8 hyperphosphorylation after crosslinking damage.","evidence":"Selective kinase inhibitors, fractionation, phospho-specific antibodies in pol-eta-deficient cells","pmids":["18289945"],"confidence":"Medium","gaps":["Largely correlative pharmacological dissection","Specific to pol-eta-deficient/crosslinker context"]},{"year":2010,"claim":"Defined PP4 as the phosphatase that reverses RPA2 phosphorylation and showed dephosphorylation is required for RAD51 loading and HR, establishing the dynamic phospho-cycle's functional importance.","evidence":"In vitro phosphatase assay, PP4R2 knockdown, Co-IP, RAD51 foci and HR reporter assays","pmids":["20154705"],"confidence":"High","gaps":["Which specific phospho-sites must be removed for RAD51 loading not pinpointed","Timing relative to resection not resolved"]},{"year":2010,"claim":"Showed RPA2 hyperphosphorylation promotes RAD51 recruitment and HR specifically under replication stress, defining a context-dependent pro-HR role.","evidence":"Phospho-deficient mutant rescue, Co-IP with RAD51, HR reporter, foci, clonogenic survival","pmids":["20130019"],"confidence":"Medium","gaps":["Apparent tension with reports of phosphorylation suppressing HR not reconciled","Site-specific contributions not separated"]},{"year":2011,"claim":"Demonstrated DNA-PK-driven Ser4/Ser8 phosphorylation restrains unscheduled HR and delays mitotic entry, framing this modification as a brake on inappropriate recombination.","evidence":"S4A/S8A mutants, DNA-PK inhibitors, RAD51 foci, HR reporter, cell cycle analysis","pmids":["21731742"],"confidence":"Medium","gaps":["Opposing pro- and anti-HR roles of different tail phosphorylations not unified into one model","Direct molecular effector of the brake unknown"]},{"year":2013,"claim":"Revealed translational control of RPA2 via an IRES bound and repressed by eIF3a, adding a layer of expression regulation during the DNA damage response.","evidence":"IRES reporter assays, eIF3a RNA binding, eIF3a knockdown, polysome profiling","pmids":["23393223"],"confidence":"Medium","gaps":["How damage signaling alters this IRES control mechanistically not defined","Physiological impact on RPA2 protein pools under stress not quantified"]},{"year":2017,"claim":"Identified a non-canonical role in which RPA2 binds menin and disrupts the menin–NF-kB p65 complex to derepress oncogenic transcription.","evidence":"Co-IP/binding assays, RPA2 overexpression and knockdown, NF-kB reporter and target immunoblots","pmids":["28007956"],"confidence":"Medium","gaps":["Whether this requires RPA2's DNA-binding/repair functions unclear","Direct vs. complex-mediated menin contact not structurally defined"]},{"year":2019,"claim":"Established HERC2 as an E3 ligase that controls levels of ATR-phosphorylated (Ser33) RPA2 and suppresses G-quadruplex structures epistatically with RPA.","evidence":"Co-IP, HERC2 C-terminal rescue, phospho-immunoblotting, ATR inhibitor, siRNA epistasis for G4 suppression","pmids":["31582797"],"confidence":"Medium","gaps":["Ubiquitin linkage type and degradation route not fully defined","Direct ubiquitination of RPA2 by HERC2 not reconstituted"]},{"year":2021,"claim":"Defined the RPA2 winged-helix domain as a direct interaction module for repair enzymes, mechanistically coupling RPA-coated ssDNA to UNG2-mediated uracil excision under PTM control.","evidence":"In vitro uracil excision on RPA-coated ssDNA, WH-domain mutants, structural/NMR analysis, UNG ubiquitination/phosphorylation modulation","pmids":["33784377"],"confidence":"High","gaps":["Functional roles of the six additional WH-binding partners not characterized","Cellular consequence of disrupting WH-UNG2 contact not measured"]},{"year":2024,"claim":"Connected an RPA2 missense variant to human disease, showing reduced RFWD3 binding and RPA ubiquitination drives telomeric RPA accumulation and a telomere biology disorder.","evidence":"Y256C knock-in cells, telomere length, RPA localization, ATR activation and ubiquitination assays","pmids":["39231615"],"confidence":"Medium","gaps":["Why telomeric RPA accumulation fails to trigger ATR not mechanistically resolved","Inheritance and penetrance details beyond engineered cells limited"]},{"year":2024,"claim":"Identified O-GlcNAcylation at Ser4/Ser8 as a modification that competes with phosphorylation and dampens Chk1 checkpoint activation.","evidence":"HCD mass spectrometry site mapping, OGT Co-IP, phospho/O-GlcNAc immunoblotting, etoposide, Chk1 and cell cycle assays","pmids":["39491647"],"confidence":"Medium","gaps":["Stoichiometry of the PTM switch in vivo not quantified","Whether O-GlcNAc also affects DNA binding not tested"]},{"year":2024,"claim":"Reported AXL-mediated tyrosine phosphorylation of RPA2 at Tyr9 promoting CHK1 activation and HR in hepatocellular carcinoma.","evidence":"Co-IP, phospho-specific immunoblotting, AXL inhibitor, siRNA, HR efficiency assay","pmids":["39281567"],"confidence":"Low","gaps":["Tyr9 site not validated by mutagenesis","Single Co-IP without reciprocal/structural confirmation"]},{"year":2025,"claim":"Resolved a switchable ubiquitin code on RPA2: TRIM21 deposits K63 linkages basally, and ATR phosphorylation of TRIM21 triggers a K6-linkage shift that stabilizes RPA2–ATRIP and supports HR.","evidence":"Co-IP, linkage-specific ubiquitination assays, TRIM21 S41 phospho-mutant, siRNA, HR reporter, ATR kinase assay","pmids":["39900724"],"confidence":"Medium","gaps":["Reader proteins distinguishing K63 vs K6 chains not identified","Relationship to HERC2/RFWD3 ubiquitin events not integrated"]},{"year":2025,"claim":"Identified TTK as a kinase phosphorylating RPA2 at Ser33 to activate ATR and drive HR, linking RPA2 modification to PARP inhibitor resistance.","evidence":"Co-IP, phospho-Ser33 immunoblotting, TTK knockdown/inhibitor, ATR assays, in vitro and in vivo HR assays","pmids":["40617868"],"confidence":"Medium","gaps":["How TTK-driven Ser33 differs functionally from ATR-driven Ser33 not resolved","Direct vs. ATR-relayed phosphorylation not fully separated"]},{"year":2025,"claim":"Showed a CSDE1–eIF3a axis upregulates RPA2 translation to enhance NER/HR and suppress cGAS-STING signaling, contributing to genotoxic drug resistance.","evidence":"Biotin-RNA pulldown, EMSA, Co-IP, CSDE1 knockout mice, DNA damage reporter assays","pmids":["40398074"],"confidence":"Medium","gaps":["Reconciliation with eIF3a's earlier reported suppressive IRES role not addressed","Direct effect on RPA2 protein levels in tumors not quantified"]},{"year":null,"claim":"How the many overlapping RPA2 modifications—ATR/DNA-PK/TTK phosphorylation, O-GlcNAcylation, and HERC2/TRIM21/RFWD3 ubiquitination—are temporally and spatially integrated to dictate replication-vs-HR pathway choice remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model orders these PTMs across the damage response","Crosstalk between distinct ubiquitin ligases on RPA2 not reconstituted","Apparent opposing pro- and anti-HR effects of tail phosphorylation not fully reconciled"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[10,5]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,10]}],"localization":[{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[0,6]},{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[1,3,4,10]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[0,2]},{"term_id":"R-HSA-8953897","term_label":"Cellular responses to stimuli","supporting_discovery_ids":[0,13,15]}],"complexes":["RPA heterotrimer"],"partners":["RAD51","MRE11","RFWD3","HERC2","TRIM21","UNG2","OGT","TTK"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P15927","full_name":"Replication protein A 32 kDa subunit","aliases":["Replication factor A protein 2","RF-A protein 2","Replication protein A 34 kDa subunit","RP-A p34"],"length_aa":270,"mass_kda":29.2,"function":"As part of the heterotrimeric replication protein A complex (RPA/RP-A), binds and stabilizes single-stranded DNA intermediates that form during DNA replication or upon DNA stress. It prevents their reannealing and in parallel, recruits and activates different proteins and complexes involved in DNA metabolism. Thereby, it plays an essential role both in DNA replication and the cellular response to DNA damage. In the cellular response to DNA damage, the RPA complex controls DNA repair and DNA damage checkpoint activation. Through recruitment of ATRIP activates the ATR kinase a master regulator of the DNA damage response. It is required for the recruitment of the DNA double-strand break repair factors RAD51 and RAD52 to chromatin in response to DNA damage. Also recruits to sites of DNA damage proteins like XPA and XPG that are involved in nucleotide excision repair and is required for this mechanism of DNA repair. Also plays a role in base excision repair (BER) probably through interaction with UNG. Also recruits SMARCAL1/HARP, which is involved in replication fork restart, to sites of DNA damage. May also play a role in telomere maintenance. RPA stimulates 5'-3' helicase activity of BRIP1/FANCJ (PubMed:17596542)","subcellular_location":"Nucleus; Nucleus, PML body","url":"https://www.uniprot.org/uniprotkb/P15927/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/RPA2","classification":"Common Essential","n_dependent_lines":1205,"n_total_lines":1208,"dependency_fraction":0.9975165562913907},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"CAPZB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RPA2","total_profiled":1310},"omim":[{"mim_id":"619949","title":"SPERMATOGENIC FAILURE 75; SPGF75","url":"https://www.omim.org/entry/619949"},{"mim_id":"618038","title":"SHORTAGE IN CHIASMATA 1; SHOC1","url":"https://www.omim.org/entry/618038"},{"mim_id":"617884","title":"HEPATOMA-DERIVED GROWTH FACTOR-LIKE PROTEIN 2; HDGFL2","url":"https://www.omim.org/entry/617884"},{"mim_id":"617784","title":"FANCONI ANEMIA, COMPLEMENTATION GROUP W; FANCW","url":"https://www.omim.org/entry/617784"},{"mim_id":"617670","title":"MEIOSIS-SPECIFIC PROTEIN WITH OB DOMAINS; MEIOB","url":"https://www.omim.org/entry/617670"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Nuclear bodies","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/RPA2"},"hgnc":{"alias_symbol":[],"prev_symbol":[]},"alphafold":{"accession":"P15927","domains":[{"cath_id":"2.40.50.140","chopping":"47-172","consensus_level":"high","plddt":92.3314,"start":47,"end":172},{"cath_id":"1.10.10.10","chopping":"208-267","consensus_level":"high","plddt":93.8537,"start":208,"end":267}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P15927","model_url":"https://alphafold.ebi.ac.uk/files/AF-P15927-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P15927-F1-predicted_aligned_error_v6.png","plddt_mean":79.31},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RPA2","jax_strain_url":"https://www.jax.org/strain/search?query=RPA2"},"sequence":{"accession":"P15927","fasta_url":"https://rest.uniprot.org/uniprotkb/P15927.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P15927/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P15927"}},"corpus_meta":[{"pmid":"17035231","id":"PMC_17035231","title":"RPA2 is a direct downstream target for ATR to regulate the S-phase checkpoint.","date":"2006","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/17035231","citation_count":152,"is_preprint":false},{"pmid":"20154705","id":"PMC_20154705","title":"A PP4 phosphatase complex dephosphorylates RPA2 to facilitate DNA repair via homologous recombination.","date":"2010","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/20154705","citation_count":126,"is_preprint":false},{"pmid":"20008938","id":"PMC_20008938","title":"Stn1-Ten1 is an Rpa2-Rpa3-like complex at telomeres.","date":"2009","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/20008938","citation_count":112,"is_preprint":false},{"pmid":"11479296","id":"PMC_11479296","title":"Functional analysis of the four DNA binding domains of replication protein A. 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RPA2 on chromatin at Thr21 and Ser33 in response to UV-induced replication fork stalling, and phospho-mimetic mutations at these ATR-dependent sites impair RPA2 association with replication centers, mechanistically linking ATR phosphorylation of RPA2 to inhibition of DNA replication in S-phase.\",\n      \"method\": \"Phospho-site mutagenesis (T21A, S33A and phospho-mimetic alleles), chromatin fractionation, DNA synthesis assays, ATR-dependent kinase assays in human cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — site-directed mutagenesis with functional readout (DNA synthesis inhibition, replication center association), multiple orthogonal approaches in a single focused study\",\n      \"pmids\": [\"17035231\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"Protein phosphatase 4 (PP4), via its regulatory subunit PP4R2, dephosphorylates RPA2 in vitro and in cells; PP4R2 mediates a DNA damage-dependent physical association between RPA2 and the PP4C catalytic subunit. PP4-mediated dephosphorylation of RPA2 is required for RAD51 loading and efficient homologous recombination (HR) after DSBs.\",\n      \"method\": \"In vitro phosphatase assay with purified PP4 and phospho-RPA2, siRNA knockdown of PP4R2, co-immunoprecipitation, RAD51 foci assay, HR reporter assay\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — in vitro dephosphorylation assay plus reciprocal Co-IP plus functional HR assay, multiple orthogonal methods in one study\",\n      \"pmids\": [\"20154705\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"The RPA2 subunit contains OB-fold DNA-binding domain D (DBD-D) which engages ssDNA substrates of ≥23–27 nucleotides; inactivation of DBD-D by mutation of conserved aromatic stacking residues has little effect on short substrates but abolishes RPA contact with oligonucleotides ≥27 nt, supporting a sequential binding model where DBD-D extends the footprint on longer ssDNA.\",\n      \"method\": \"In vitro ssDNA binding assays with purified recombinant yeast RPA carrying single-DBD inactivating mutations, protein-DNA crosslinking\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro binding with mutagenesis and crosslinking, multiple substrates tested; single lab but rigorous biochemistry\",\n      \"pmids\": [\"11479296\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2010,\n      \"finding\": \"RPA2 hyperphosphorylation (induced by hydroxyurea-mediated replication arrest) promotes association of RPA2 with ssDNA and RAD51, is required for RAD51 recruitment and HR-mediated repair of HU-induced damage, and its loss leads to chromosomal aberrations and reduced viability specifically under replication stress but not after ionizing radiation.\",\n      \"method\": \"Phosphorylation-deficient RPA2 mutant expression, co-immunoprecipitation with RAD51, HR reporter assays, immunofluorescence for RAD51 foci, clonogenic survival\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean mutant rescue with multiple functional readouts (HR, foci, survival), single lab\",\n      \"pmids\": [\"20130019\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"DNA-PK phosphorylates RPA2 at Ser4 and Ser8 primarily in response to DSBs; this hyperphosphorylation suppresses unscheduled homologous recombination (evidenced by increased RAD51 foci and HR in S4A/S8A mutant cells) and delays mitotic entry, allowing proper DSB repair.\",\n      \"method\": \"S4A/S8A phospho-mutant RPA2 expression, DNA-PK inhibitors, RAD51 foci quantification, HR reporter assay, cell cycle analysis\",\n      \"journal\": \"PloS one\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — phospho-mutant cells with pharmacological inhibitor confirmation, multiple readouts, single lab\",\n      \"pmids\": [\"21731742\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"RPA2 phosphorylation (phosphorylated or phosphomimetic RPA) weakens the direct physical interaction between RPA and the MRN complex (MRE11, RAD50, NBS1), and the N-terminal OB-fold of RPA1 (requiring Arg31 and Arg41) is the critical determinant of the RPA–MRN protein–protein interaction.\",\n      \"method\": \"Pulldown assays with purified proteins, co-immunoprecipitation, RPA1 N-terminal deletion and point mutants (R31A, R41A), phosphomimetic RPA2 substitution\",\n      \"journal\": \"Biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct protein-protein interaction with purified components plus mutagenesis, single lab\",\n      \"pmids\": [\"19586055\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"In DNA polymerase eta-deficient cells, cisplatin- and oxaliplatin-induced hyperphosphorylation of RPA2 at Ser4/Ser8 is mediated by DNA-PK (blocked by NU7441) rather than ATM; ATR is required for initial RPA2 recruitment to chromatin and subsequently enables DNA-PK-mediated Ser4/Ser8 phosphorylation.\",\n      \"method\": \"Selective kinase inhibitors (NU7441 for DNA-PK, KU-55933 for ATM, CGK733 for ATM/ATR), immunofluorescence, subcellular fractionation, phospho-specific antibodies\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — pharmacological dissection of kinase contributions with fractionation confirmation, single lab\",\n      \"pmids\": [\"18289945\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"53BP1 physically associates with RPA1 and RPA2 (interaction disrupted by camptothecin-induced DNA damage), and dominant-negative 53BP1 fragments or 53BP1 siRNA knockdown inhibit camptothecin-induced RPA2 hyperphosphorylation, placing 53BP1 upstream of RPA2 phosphorylation in the DNA damage response.\",\n      \"method\": \"Co-immunoprecipitation followed by tandem MS identification, immunoblotting, dominant-negative 53BP1 stable cell lines, siRNA knockdown, RPA2 phosphorylation assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — reciprocal Co-IP with MS confirmation plus genetic (DN and siRNA) functional follow-up; single lab\",\n      \"pmids\": [\"15856006\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2013,\n      \"finding\": \"RPA2 translation is regulated via an internal ribosome entry site (IRES) located −50 to −150 bases upstream of the start codon; eIF3a directly binds this IRES element and suppresses RPA2 synthesis, providing a translational control mechanism for RPA2 expression during DNA damage response.\",\n      \"method\": \"IRES reporter assays, eIF3a RNA binding (EMSA/pulldown), siRNA knockdown of eIF3a, polysome profiling, DNA damage treatment\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct RNA-protein binding assay plus functional IRES reporter, single lab, two methods\",\n      \"pmids\": [\"23393223\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"HERC2 E3 ubiquitin ligase interacts with RPA2 via its C-terminal HECT domain and mediates ubiquitination-dependent degradation of ATR-phosphorylated RPA2 (Ser33); HERC2 depletion inhibits ATR-mediated Ser33 phosphorylation under low-level replication stress, while loss of HERC2 catalytic activity causes constitutively elevated Ser33-phospho-RPA2. HERC2 E3 activity is epistatic to RPA in suppression of G-quadruplex DNA structures.\",\n      \"method\": \"Co-immunoprecipitation, siRNA knockdown and rescue with HERC2 C-terminal fragment, phospho-specific immunoblotting, ATR inhibitor treatment, siRNA epistasis for G4 suppression\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus rescue experiment plus epistasis analysis plus pharmacological inhibitor, single lab\",\n      \"pmids\": [\"31582797\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"The flexible winged-helix (WH) domain of RPA2 directly interacts with the N-terminal RPA-binding helix of UNG2 (uracil-DNA glycosylase), enabling efficient excision of uracil from RPA-coated ssDNA; this interaction is promoted by mono-ubiquitination of UNG and diminished by cell-cycle-regulated phosphorylations on UNG. Six additional DNA repair/replication fork remodeling proteins also bind the RPA2-WH domain.\",\n      \"method\": \"In vitro uracil excision assays on RPA-coated ssDNA, binding/interaction assays with WH domain mutants, NMR/structural analysis of interaction, ubiquitination and phosphorylation of UNG modulating the interaction\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstituted activity assay plus mutagenesis of WH domain plus identification of binding helix in UNG, multiple methods in single study\",\n      \"pmids\": [\"33784377\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RPA2 physically interacts with menin (the MEN1 tumor suppressor protein); ectopic RPA2 expression disrupts the menin–NF-κB p65 complex, relieving menin's inhibitory effect on NF-κB-regulated transcription and promoting oncogenic gene expression. Conversely, RPA2 knockdown enhances the menin–p65 complex and suppresses NF-κB target genes.\",\n      \"method\": \"Co-immunoprecipitation/binding assays, RPA2 overexpression and siRNA knockdown, NF-κB reporter assay, immunoblotting for NF-κB targets\",\n      \"journal\": \"Carcinogenesis\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — Co-IP plus functional reporter assay plus bidirectional manipulation (OE and KD), single lab\",\n      \"pmids\": [\"28007956\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"A heterozygous Y256C variant in RPA2 reduces RPA2 affinity for RFWD3 (ubiquitin ligase) and reduces RPA ubiquitination, causing accumulation of RPA at telomeres without triggering ATR activation, resulting in short and dysfunctional telomeres and telomere biology disorder in patients.\",\n      \"method\": \"Knock-in cell lines engineered with Y256C mutation, telomere length measurement, RPA telomere localization (ChIP/IF), ATR activation assays, RPA–RFWD3 interaction assays, ubiquitination assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — engineered knock-in cells with multiple functional readouts (telomere length, RPA foci, ATR signaling, ubiquitination), single study\",\n      \"pmids\": [\"39231615\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"O-GlcNAcylation of RPA2 by OGT occurs at Ser4/Ser8 (mapped by mass spectrometry) and directly antagonizes phosphorylation at these sites; OGT interacts with RPA2 and this association is reduced by etoposide treatment. Ser4/Ser8 O-GlcNAcylation impairs downstream Chk1 activation and promotes inappropriate cell cycle progression, indicating a checkpoint defect.\",\n      \"method\": \"HCD mass spectrometry mapping of O-GlcNAc sites, OGT co-immunoprecipitation, phospho-specific and O-GlcNAc-specific immunoblotting, etoposide treatment, Chk1 activation assay, cell cycle analysis\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1–2 / Moderate — MS-based site mapping plus Co-IP plus functional checkpoint assay, single lab, multiple methods\",\n      \"pmids\": [\"39491647\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TRIM21 mediates K63-linked ubiquitination of RPA2 under basal conditions; upon DNA damage, ATR phosphorylates TRIM21 at Ser41, causing dissociation of the TRIM21–RPA2 complex and a shift from K63- to K6-linked ubiquitination of RPA2. K6-linked ubiquitination stabilizes the RPA2–ATRIP complex and is required for efficient homologous recombination repair.\",\n      \"method\": \"Co-immunoprecipitation, ubiquitination linkage-specific assays, TRIM21 S41 phospho-mutant expression, siRNA knockdown, HR repair reporter assay, ATR kinase assay\",\n      \"journal\": \"Oncogene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP plus ubiquitin linkage assays plus HR reporter, single lab, multiple methods\",\n      \"pmids\": [\"39900724\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"TTK kinase directly interacts with RPA2 and phosphorylates RPA2 at Ser33, which activates the ATR signaling pathway and promotes homologous recombination-mediated repair, contributing to PARP inhibitor resistance in ovarian cancer cells.\",\n      \"method\": \"Co-immunoprecipitation of TTK–RPA2, phospho-Ser33 immunoblotting, TTK knockdown and inhibitor treatment, ATR pathway activation assays, in vitro and in vivo HR assays\",\n      \"journal\": \"Communications biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — direct physical interaction plus phosphorylation site-specific readout plus in vivo model confirmation, single lab\",\n      \"pmids\": [\"40617868\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"CSDE1 forms a ternary complex with eIF3a protein and RPA2 mRNA (confirmed by biotin pulldown, EMSA and co-IP), upregulating RPA2 translation; this CSDE1-eIF3a-RPA2 regulatory axis enhances nucleotide excision repair and homologous recombination and suppresses cGAS-STING signaling, conferring genotoxic drug resistance.\",\n      \"method\": \"Biotin-RNA pulldown, EMSA, co-immunoprecipitation, CSDE1 knockout mouse models, DNA damage reporter assays\",\n      \"journal\": \"Drug resistance updates\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct RNA-protein binding demonstrated by three orthogonal methods plus in vivo knockout validation, single lab\",\n      \"pmids\": [\"40398074\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"AXL receptor tyrosine kinase physically interacts with RPA2, promotes its recruitment to DNA damage sites, and tyrosinates RPA2 at Tyr9, which in turn promotes CHK1 phosphorylation and strengthens HR repair capacity in hepatocellular carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation of AXL–RPA2, phospho-specific immunoblotting, AXL kinase inhibitor (bemcentinib), siRNA knockdown, HR efficiency assay\",\n      \"journal\": \"Heliyon\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single Co-IP plus inhibitor data, tyrosination site not validated by mutagenesis, single lab\",\n      \"pmids\": [\"39281567\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RPA2 (the 32 kDa middle subunit of the heterotrimeric RPA complex) binds ssDNA through its OB-fold domain D to extend RPA's footprint on substrates >23 nt and interacts with repair/replication proteins via its winged-helix domain; its N-terminal tail is extensively phosphorylated by ATR (Thr21, Ser33), DNA-PK (Ser4, Ser8), and TTK (Ser33), with phosphorylation coordinating inhibition of replication initiation, regulation of RPA–MRN interactions, control of RAD51 loading and HR fidelity, and telomere maintenance, while counterbalancing modifications including PP4-mediated dephosphorylation, HERC2- and TRIM21-mediated ubiquitination (K63 vs. K6 linkage switch), and OGT-mediated O-GlcNAcylation at Ser4/Ser8 collectively fine-tune checkpoint activation, HR efficiency, and genome stability.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RPA2 is the middle subunit of the heterotrimeric single-stranded DNA-binding protein RPA, contributing an OB-fold DNA-binding domain (DBD-D) that extends the RPA footprint onto ssDNA substrates longer than ~23 nucleotides [#2] and a flexible winged-helix (WH) domain that serves as a docking platform for repair and replication-fork enzymes, including UNG2, whose RPA-binding helix engages the WH domain to enable uracil excision from RPA-coated ssDNA [#10]. The dominant mechanistic theme is regulation of the DNA damage response through the heavily modified RPA2 N-terminal tail: ATR phosphorylates Thr21/Ser33 upon replication fork stalling to inhibit replication initiation [#0], DNA-PK phosphorylates Ser4/Ser8 to suppress untimely homologous recombination and delay mitotic entry [#4], and these events are dynamically reversed by PP4-mediated dephosphorylation, which is itself required for RAD51 loading and efficient HR [#1]. RPA2 phosphorylation status gates protein interactions central to repair-pathway choice, weakening the RPA–MRN association [#5] while promoting RPA2 binding to RAD51 to drive HR under replication stress [#3]. Beyond phosphorylation, RPA2 function is tuned by a switchable ubiquitin code—TRIM21-mediated K63 linkage under basal conditions converting to K6 linkage after ATR signaling to stabilize the RPA2–ATRIP complex and support HR [#14]—and by O-GlcNAcylation at Ser4/Ser8 that antagonizes phosphorylation and impairs Chk1 checkpoint activation [#13]. A heterozygous RPA2 Y256C variant that weakens RFWD3 binding and reduces RPA ubiquitination causes telomeric RPA accumulation, short dysfunctional telomeres, and a telomere biology disorder [#12].\",\n  \"teleology\": [\n    {\n      \"year\": 2001,\n      \"claim\": \"Established the biochemical contribution of the RPA2 subunit to substrate engagement, showing its OB-fold extends RPA's grip onto longer ssDNA.\",\n      \"evidence\": \"In vitro ssDNA binding and crosslinking with purified RPA carrying single-DBD inactivating mutations\",\n      \"pmids\": [\"11479296\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Performed with yeast RPA; human-specific quantitative parameters not addressed\", \"Does not connect DBD-D occupancy to downstream repair outcomes\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Placed 53BP1 upstream of RPA2 hyperphosphorylation, defining an early signaling input to the RPA2 modification cascade.\",\n      \"evidence\": \"Co-IP/MS, dominant-negative and siRNA knockdown of 53BP1, RPA2 phosphorylation assay after camptothecin\",\n      \"pmids\": [\"15856006\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not identify the responsible kinase downstream of 53BP1\", \"Direct vs. indirect basis of the interaction not resolved\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Identified ATR as a direct RPA2 kinase at Thr21/Ser33 and linked this modification to inhibition of replication during fork stalling.\",\n      \"evidence\": \"Phospho-site and phospho-mimetic mutagenesis, chromatin fractionation, DNA synthesis assays in human cells\",\n      \"pmids\": [\"17035231\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular mechanism by which phospho-RPA2 dissociates from replication centers not defined\", \"Interplay with other tail sites not addressed\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Showed RPA2 phosphorylation acts as a switch that weakens the RPA–MRN interaction, and mapped the interaction determinant to the RPA1 N-terminal OB-fold.\",\n      \"evidence\": \"Pulldowns/Co-IP with purified proteins, RPA1 deletion and R31A/R41A mutants, phosphomimetic RPA2\",\n      \"pmids\": [\"19586055\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Cellular consequence of MRN release for resection kinetics not directly measured\", \"Which physiological kinase drives this in vivo not established here\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Dissected the kinase hierarchy showing ATR enables initial chromatin recruitment that licenses DNA-PK-mediated Ser4/Ser8 hyperphosphorylation after crosslinking damage.\",\n      \"evidence\": \"Selective kinase inhibitors, fractionation, phospho-specific antibodies in pol-eta-deficient cells\",\n      \"pmids\": [\"18289945\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Largely correlative pharmacological dissection\", \"Specific to pol-eta-deficient/crosslinker context\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Defined PP4 as the phosphatase that reverses RPA2 phosphorylation and showed dephosphorylation is required for RAD51 loading and HR, establishing the dynamic phospho-cycle's functional importance.\",\n      \"evidence\": \"In vitro phosphatase assay, PP4R2 knockdown, Co-IP, RAD51 foci and HR reporter assays\",\n      \"pmids\": [\"20154705\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Which specific phospho-sites must be removed for RAD51 loading not pinpointed\", \"Timing relative to resection not resolved\"]\n    },\n    {\n      \"year\": 2010,\n      \"claim\": \"Showed RPA2 hyperphosphorylation promotes RAD51 recruitment and HR specifically under replication stress, defining a context-dependent pro-HR role.\",\n      \"evidence\": \"Phospho-deficient mutant rescue, Co-IP with RAD51, HR reporter, foci, clonogenic survival\",\n      \"pmids\": [\"20130019\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Apparent tension with reports of phosphorylation suppressing HR not reconciled\", \"Site-specific contributions not separated\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Demonstrated DNA-PK-driven Ser4/Ser8 phosphorylation restrains unscheduled HR and delays mitotic entry, framing this modification as a brake on inappropriate recombination.\",\n      \"evidence\": \"S4A/S8A mutants, DNA-PK inhibitors, RAD51 foci, HR reporter, cell cycle analysis\",\n      \"pmids\": [\"21731742\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Opposing pro- and anti-HR roles of different tail phosphorylations not unified into one model\", \"Direct molecular effector of the brake unknown\"]\n    },\n    {\n      \"year\": 2013,\n      \"claim\": \"Revealed translational control of RPA2 via an IRES bound and repressed by eIF3a, adding a layer of expression regulation during the DNA damage response.\",\n      \"evidence\": \"IRES reporter assays, eIF3a RNA binding, eIF3a knockdown, polysome profiling\",\n      \"pmids\": [\"23393223\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How damage signaling alters this IRES control mechanistically not defined\", \"Physiological impact on RPA2 protein pools under stress not quantified\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identified a non-canonical role in which RPA2 binds menin and disrupts the menin–NF-kB p65 complex to derepress oncogenic transcription.\",\n      \"evidence\": \"Co-IP/binding assays, RPA2 overexpression and knockdown, NF-kB reporter and target immunoblots\",\n      \"pmids\": [\"28007956\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether this requires RPA2's DNA-binding/repair functions unclear\", \"Direct vs. complex-mediated menin contact not structurally defined\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established HERC2 as an E3 ligase that controls levels of ATR-phosphorylated (Ser33) RPA2 and suppresses G-quadruplex structures epistatically with RPA.\",\n      \"evidence\": \"Co-IP, HERC2 C-terminal rescue, phospho-immunoblotting, ATR inhibitor, siRNA epistasis for G4 suppression\",\n      \"pmids\": [\"31582797\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Ubiquitin linkage type and degradation route not fully defined\", \"Direct ubiquitination of RPA2 by HERC2 not reconstituted\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the RPA2 winged-helix domain as a direct interaction module for repair enzymes, mechanistically coupling RPA-coated ssDNA to UNG2-mediated uracil excision under PTM control.\",\n      \"evidence\": \"In vitro uracil excision on RPA-coated ssDNA, WH-domain mutants, structural/NMR analysis, UNG ubiquitination/phosphorylation modulation\",\n      \"pmids\": [\"33784377\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Functional roles of the six additional WH-binding partners not characterized\", \"Cellular consequence of disrupting WH-UNG2 contact not measured\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Connected an RPA2 missense variant to human disease, showing reduced RFWD3 binding and RPA ubiquitination drives telomeric RPA accumulation and a telomere biology disorder.\",\n      \"evidence\": \"Y256C knock-in cells, telomere length, RPA localization, ATR activation and ubiquitination assays\",\n      \"pmids\": [\"39231615\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Why telomeric RPA accumulation fails to trigger ATR not mechanistically resolved\", \"Inheritance and penetrance details beyond engineered cells limited\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified O-GlcNAcylation at Ser4/Ser8 as a modification that competes with phosphorylation and dampens Chk1 checkpoint activation.\",\n      \"evidence\": \"HCD mass spectrometry site mapping, OGT Co-IP, phospho/O-GlcNAc immunoblotting, etoposide, Chk1 and cell cycle assays\",\n      \"pmids\": [\"39491647\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Stoichiometry of the PTM switch in vivo not quantified\", \"Whether O-GlcNAc also affects DNA binding not tested\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Reported AXL-mediated tyrosine phosphorylation of RPA2 at Tyr9 promoting CHK1 activation and HR in hepatocellular carcinoma.\",\n      \"evidence\": \"Co-IP, phospho-specific immunoblotting, AXL inhibitor, siRNA, HR efficiency assay\",\n      \"pmids\": [\"39281567\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Tyr9 site not validated by mutagenesis\", \"Single Co-IP without reciprocal/structural confirmation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Resolved a switchable ubiquitin code on RPA2: TRIM21 deposits K63 linkages basally, and ATR phosphorylation of TRIM21 triggers a K6-linkage shift that stabilizes RPA2–ATRIP and supports HR.\",\n      \"evidence\": \"Co-IP, linkage-specific ubiquitination assays, TRIM21 S41 phospho-mutant, siRNA, HR reporter, ATR kinase assay\",\n      \"pmids\": [\"39900724\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reader proteins distinguishing K63 vs K6 chains not identified\", \"Relationship to HERC2/RFWD3 ubiquitin events not integrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identified TTK as a kinase phosphorylating RPA2 at Ser33 to activate ATR and drive HR, linking RPA2 modification to PARP inhibitor resistance.\",\n      \"evidence\": \"Co-IP, phospho-Ser33 immunoblotting, TTK knockdown/inhibitor, ATR assays, in vitro and in vivo HR assays\",\n      \"pmids\": [\"40617868\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"How TTK-driven Ser33 differs functionally from ATR-driven Ser33 not resolved\", \"Direct vs. ATR-relayed phosphorylation not fully separated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed a CSDE1–eIF3a axis upregulates RPA2 translation to enhance NER/HR and suppress cGAS-STING signaling, contributing to genotoxic drug resistance.\",\n      \"evidence\": \"Biotin-RNA pulldown, EMSA, Co-IP, CSDE1 knockout mice, DNA damage reporter assays\",\n      \"pmids\": [\"40398074\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Reconciliation with eIF3a's earlier reported suppressive IRES role not addressed\", \"Direct effect on RPA2 protein levels in tumors not quantified\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the many overlapping RPA2 modifications—ATR/DNA-PK/TTK phosphorylation, O-GlcNAcylation, and HERC2/TRIM21/RFWD3 ubiquitination—are temporally and spatially integrated to dictate replication-vs-HR pathway choice remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model orders these PTMs across the damage response\", \"Crosstalk between distinct ubiquitin ligases on RPA2 not reconstituted\", \"Apparent opposing pro- and anti-HR effects of tail phosphorylation not fully reconciled\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [10, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 10]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [1, 3, 4, 10]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [0, 2]},\n      {\"term_id\": \"R-HSA-8953897\", \"supporting_discovery_ids\": [0, 13, 15]}\n    ],\n    \"complexes\": [\"RPA heterotrimer\"],\n    \"partners\": [\"RAD51\", \"MRE11\", \"RFWD3\", \"HERC2\", \"TRIM21\", \"UNG2\", \"OGT\", \"TTK\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}