{"gene":"RAD51AP1","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2007,"finding":"RAD51AP1 binds both dsDNA and D-loop structures and, only when able to interact with RAD51, greatly stimulates the RAD51-mediated D-loop reaction. RAD51AP1 functions at a step subsequent to assembly of the RAD51-ssDNA nucleoprotein filament. RAD51AP1 is epistatic to the HR protein XRCC3.","method":"In vitro D-loop assay with purified RAD51AP1, EMSA for DNA binding, RNAi knockdown with HR repair assay and chromosomal break analysis, epistasis analysis with XRCC3","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro D-loop assay with purified protein, mutagenesis, cellular epistasis, replicated in companion paper same year","pmids":["17996711"],"is_preprint":false},{"year":2007,"finding":"RAD51AP1 is a structure-specific DNA binding protein with selective affinity for branched-DNA structures (obligatory intermediates during joint molecule formation) and stimulates RAD51-mediated joint molecule formation through the combination of structure-specific DNA binding and direct physical contact with RAD51.","method":"In vitro joint molecule formation assay, DNA binding assays (EMSA) with branched vs. linear substrates, Co-IP/physical interaction mapping, cellular DNA damage sensitivity assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro assay, structure-specific binding demonstrated biochemically, replicated by companion paper same year","pmids":["17996710"],"is_preprint":false},{"year":2011,"finding":"RAD51AP1 physically associates with the meiosis-specific recombinase DMC1 and stimulates the DMC1-mediated D-loop reaction by enhancing DMC1 presynaptic filament capacity to capture duplex-DNA and assemble the synaptic complex. Functional cooperation requires complex formation between DMC1 and RAD51AP1, and distinct epitopes in RAD51AP1 mediate interactions with RAD51 and DMC1. RAD51AP1 foci colocalize with a subset of DMC1 foci in mouse spermatocytes.","method":"In vitro D-loop assay with purified DMC1 and RAD51AP1, synaptic complex assembly assay, Co-IP, immunofluorescence in mouse spermatocytes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro D-loop and synaptic complex assays, confirmed by cellular colocalization, multiple orthogonal methods in one study","pmids":["21307306"],"is_preprint":false},{"year":2011,"finding":"A highly conserved WVPP motif in RAD51AP1 is critical for DMC1 interaction but dispensable for RAD51 association, demonstrating that RAD51AP1 uses distinct epitopes to interact with RAD51 versus DMC1. This WVPP motif is reminiscent of the FVPP motif in BRCA2 that mediates DMC1 interaction.","method":"Series of truncation and point mutations in RAD51AP1 analyzed by Co-IP and interaction assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis with functional interaction mapping, multiple mutants tested, single lab","pmids":["21903585"],"is_preprint":false},{"year":2012,"finding":"RAD51AP1 harbors two distinct DNA binding domains that are both required for maximal protein activity under physiological conditions; mutant variants impaired in either or both DNA binding domains are non-functional in cells.","method":"Domain mapping by truncation and point mutagenesis, EMSA, cellular complementation assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis, in vitro DNA binding, and cellular functional assays, multiple orthogonal methods in one study","pmids":["22375013"],"is_preprint":false},{"year":2006,"finding":"RAD51AP1/PIR51 and RAD51AP2 use the same conserved C-terminal structural motif (~57 residues in RAD51AP2, mapped to 40 aa in RAD51AP1) for RAD51 binding. Point mutations in this motif abolish RAD51 interaction.","method":"Yeast two-hybrid, truncation and point mutation analysis in HEK293 cells, Co-IP","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction mapping using multiple truncations and point mutants, two-hybrid plus cellular Co-IP, single lab","pmids":["16990250"],"is_preprint":false},{"year":2016,"finding":"UAF1 binds DNA and forms a dimeric complex with RAD51AP1 through SUMO-like domains in UAF1 and a SUMO-interacting motif (SIM) in RAD51AP1, and a trimeric complex with RAD51 through RAD51AP1. The RAD51AP1-UAF1 complex cooperates with RAD51 to assemble the synaptic complex and enhances RAD51-mediated homologous DNA pairing in a manner dependent on RAD51AP1 but independent of USP1.","method":"In vitro D-loop/synaptic complex assay with purified proteins, Co-IP, domain interaction mapping with SUMO-SIM mutations, cellular HR assay","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro synaptic complex and D-loop assays, biochemical interaction mapping, cellular validation, multiple orthogonal methods","pmids":["27239033"],"is_preprint":false},{"year":2016,"finding":"USP1-UAF1 complex interacts with RAD51AP1 via UAF1, which mediates the interaction; depletion of USP1 or UAF1 reduces RAD51AP1 stability. A UAF1 interaction-deficient mutant of RAD51AP1 causes persistent RAD51 foci following DNA damage, indicating RAD51AP1-UAF1 regulates a later step in HR repair.","method":"Proteomic pulldown of UAF1-interacting proteins, Co-IP, protein stability assays, RAD51 foci analysis after DNA damage, chromosomal aberration assay","journal":"Cell cycle (Georgetown, Tex.)","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal Co-IP, mutant complementation with phenotypic readout, single lab with multiple methods","pmids":["27463890"],"is_preprint":false},{"year":2019,"finding":"Efficient FANCD2 deubiquitination by the USP1-UAF1 complex requires DNA and DNA binding by UAF1. The DNA binding activity of UAF1-associated RAD51AP1 can substitute for that of UAF1 in FANCD2 deubiquitination in a reconstituted biochemical system. DNA binding by UAF1 and RAD51AP1 is important for FANCD2 deubiquitination in cells.","method":"Reconstituted biochemical deubiquitination assay with purified USP1-UAF1-RAD51AP1 and FANCD2, cellular deubiquitination assay with separation-of-function mutants","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted biochemical system, separation-of-function mutants, cellular validation, multiple orthogonal methods in one study","pmids":["31253762"],"is_preprint":false},{"year":2019,"finding":"RAD51AP1 is required for both RAD51-dependent HR and RAD52-POLD3-dependent break-induced DNA synthesis at ALT telomeres. RAD51AP1 KO in ALT+ cells causes generational telomere shortening, telomere dysfunction, and cytosolic telomeric DNA that activates cGAS. RAD51AP1 protein levels are elevated in ALT+ cells due to MMS21-associated SUMOylation; mutation of a single SUMO-targeted lysine residue perturbs telomere dynamics.","method":"RAD51AP1 KO in ALT+ cancer cells, telomere FISH, cGAS activation assay, autophagy assays, SUMOylation assay with MMS21, SUMO-site mutagenesis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO with multiple phenotypic readouts, SUMOylation biochemistry, site-specific mutagenesis with functional consequence, multiple orthogonal methods","pmids":["31400850"],"is_preprint":false},{"year":2014,"finding":"RAD51AP1 deficiency in vertebrate cells impairs DNA replication fork progression and causes increased replication origin firing. In RAD51AP1-deficient cells, resolution of DNA damage-induced RAD51 foci is greatly slowed while their formation is not impaired, placing RAD51AP1 function after RAD51 filament assembly.","method":"Targeted RAD51AP1 gene inactivation in chicken DT40 cells, DNA fiber assay for replication fork speed, RAD51 foci kinetics by immunofluorescence, complementation with human/chicken RAD51AP1","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 2 / Strong — genetic KO model, DNA fiber assay, RAD51 foci kinetics, complementation assays, multiple orthogonal methods","pmids":["25288561"],"is_preprint":false},{"year":2021,"finding":"RAD51AP1 binds to nucleosome core particles (NCPs) through a C-terminal region including its DNA-binding domain, and can promote duplex DNA capture and joint-molecule formation with chromatinized template DNA in vitro, suggesting RAD51AP1 anchors the DNA template through nucleosome affinity to the RAD51-ssDNA filament.","method":"In vitro binding assays (EMSA, pulldown) with purified NCPs and histone octamers, in vitro D-loop/joint molecule assay with chromatinized DNA, domain mapping by truncation","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — reconstituted in vitro assays with purified NCPs and chromatinized substrates, domain mapping, multiple biochemical methods, single lab","pmids":["34058198"],"is_preprint":false},{"year":2022,"finding":"RAD51AP1 interacts with TERRA RNA and uses it to generate D-loop and R-loop HR intermediates at telomeres. RAD51AP1 depletion reduces R-loop formation at telomere DNA breaks. RAD51AP1-mediated TERRA R-loop homeostasis suppresses TERRA transcription and prevents transcription-replication collisions during ALT-HDR. Both TERRA binding and this chromatin-directed function require RAD51AP1's intrinsic SUMO-SIM regulatory axis.","method":"TERRA R-loop assays in vitro and at telomeres, RAD51AP1 KD with R-loop measurement (S9.6 antibody), proteomics of RAD51AP1-associated proteins, SUMO-SIM mutant analysis","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (in vitro, cellular, proteomic), genetic KD with specific mechanistic readout, SUMO-SIM mutagenesis, two companion papers simultaneously","pmids":["36265488"],"is_preprint":false},{"year":2022,"finding":"TERRA forms R-loops in vitro and at telomeres in a RAD51AP1-dependent manner. RAD51AP1-assembled TERRA R-loops generate G-quadruplexes (G4s) at telomeres, which persist after R-loop resolution and enable D-loop formation without RAD52, orchestrating an R-to-D-loop switch that promotes break-induced replication in the RAD52-independent ALT pathway.","method":"In vitro R-loop formation assay with purified TERRA and RAD51AP1, telomeric R-loop quantification in RAD51AP1-dependent knockdown cells, G4 detection, D-loop assay in RAD52 KO cells","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — reconstituted in vitro assays, cellular validation in RAD52 KO background, G4 epistasis experiments, multiple orthogonal methods","pmids":["36265486"],"is_preprint":false},{"year":2022,"finding":"RAD51AP1 and RAD54L define two distinct sub-pathways downstream of RAD51 in HR; simultaneous deletion of RAD51AP1 and RAD54L shows synthetic sensitivity to PARP inhibitor (olaparib), mitomycin C, and hydroxyurea, establishing that the two proteins underpin non-redundant HR routes.","method":"Double KO of RAD51AP1 and RAD54L in human cancer cell lines, clonogenic survival with olaparib, MMC, hydroxyurea; comparison with RAD54B single KO","journal":"Frontiers in cell and developmental biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis via double KO, multiple genotoxic agents, single lab","pmids":["35652094"],"is_preprint":false},{"year":2024,"finding":"RAD51AP1 associates with pre-rRNA through both its N-terminus and C-terminus. Pre-rRNA colocalizes with RAD51AP1 at double-strand breaks and facilitates RAD51AP1 recruitment to DSBs. RAD51AP1 forms liquid-liquid phase separation in the presence of pre-rRNA in vitro, which may underlie RAD51AP1 foci formation.","method":"RNA immunoprecipitation, colocalization at DSBs by imaging, RNA polymerase I inhibitor treatment, in vitro phase separation assay with purified RAD51AP1 and pre-rRNA","journal":"The Journal of biological chemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — RIP, cellular colocalization, pharmacological inhibition, in vitro phase separation; single lab, multiple orthogonal methods","pmids":["38403248"],"is_preprint":false},{"year":2025,"finding":"RAD51AP1 possesses at least three RAD51-binding sites that span two adjacent RAD51 molecules. RAD51AP1 stabilizes the RAD51 N-terminal domain and protomer interface in filaments, promotes RAD51-ssDNA filament nucleation and stabilization, and stimulates strand exchange. Structural data show RAD51AP1 binding induces conformational changes promoting RAD51 DNA association and oligomerization. RAD51-ssDNA filaments expand upon ATP hydrolysis to ADP, explaining reduced RAD51-DNA binding in the ADP state.","method":"Cryo-EM structures of RAD51-ssDNA filaments with and without RAD51AP1 in Mg2+-ATP and Mg2+-ADP states, biochemical strand exchange assays, filament stabilization assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structural biology combined with biochemical reconstitution and strand exchange assays, multiple orthogonal methods","pmids":["41337480"],"is_preprint":false},{"year":2025,"finding":"RAD51AP1 activity in HDR is regulated by CDK2-mediated phosphorylation at S277 and S282. A phospho-deficient S277/282A mutant more avidly binds ssDNA, dsDNA, and nucleosome core particles and is more proficient in D-loop stimulation in vitro, but fails to rescue RAD51AP1 deficiency in cellular toxicity and DNA replication assays. A phosphomimetic S277/282D mutant fully rescues RAD51AP1 deficiency in cells, suggesting phosphorylation ensures dynamic RAD51AP1 engagement across consecutive HDR steps.","method":"Site-directed mutagenesis (S277A, S282A, S277/282D), in vitro D-loop assay, EMSA with ssDNA/dsDNA/NCP, cellular toxicity and DNA replication assays, CDK2 phosphorylation identification","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Moderate — mutagenesis combined with in vitro biochemistry, EMSA, and cellular complementation assays; CDK2 identified as the writer; multiple orthogonal methods in one study","pmids":["41534830"],"is_preprint":false},{"year":2025,"finding":"RAD51AP1 is required for TERRA R-loop formation in telomerase-expressing cells; both RAD51 and RAD51AP1 contribute non-redundant functions to TERRA R-loop formation. TERRA R-loops interfere with semiconservative DNA replication and promote break-induced replication for telomere maintenance.","method":"TERRA overexpression in telomerase+ cells, RAD51AP1 depletion, R-loop measurement, DNA replication interference assay, BIR assay","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic depletion with specific R-loop and BIR readouts, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.01.09.632133"],"is_preprint":true},{"year":2024,"finding":"E2F1 transcription factor drives RAD51AP1 expression in EGFRvIII-positive glioblastoma cells in response to TMZ treatment; RAD51AP1 promotes formation of the RAD51-UAF1 complex to activate homologous recombination and thereby confers TMZ resistance. H3K27ac and SOX9 together induce RAD51AP1 transcription in EGFRvIII cells.","method":"CRISPR/Cas9 synthetic lethal screen, ChIP-seq and ChIP-PCR for H3K27ac and SOX9 at RAD51AP1 promoter, RAD51AP1 KD and OE with HR and drug sensitivity assays","journal":"Chinese medical journal","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — CRISPR screen plus ChIP-seq/PCR validation and functional assays; single lab, multiple methods","pmids":["40211735"],"is_preprint":false}],"current_model":"RAD51AP1 is a multifunctional RAD51 accessory protein that binds branched/D-loop DNA structures and RNA (including TERRA and pre-rRNA) through two distinct DNA-binding domains, directly interacts with RAD51 via at least three binding sites spanning two adjacent RAD51 protomers to stabilize RAD51-ssDNA filaments and promote filament nucleation, synaptic complex assembly, and strand exchange; it also physically interacts with the meiotic recombinase DMC1 via a distinct WVPP motif to stimulate meiotic recombination; forms a complex with UAF1 (via a SUMO-SIM interface) that further enhances RAD51-mediated DNA pairing and participates in FANCD2 deubiquitination by the USP1-UAF1 complex; binds nucleosome core particles to promote HR on chromatinized templates; assembles TERRA-containing R-loops at ALT telomeres to generate G-quadruplexes and drive an R-to-D-loop switch enabling RAD52-independent break-induced replication; is SUMOylated by MMS21 at ALT+ cells to sustain telomere length; and is regulated by CDK2-mediated phosphorylation at S277/S282 that ensures dynamic engagement across consecutive HDR steps."},"narrative":{"mechanistic_narrative":"RAD51AP1 is a structure-specific DNA-binding accessory factor that promotes RAD51-mediated homologous recombination (HR) at a step downstream of presynaptic filament assembly [PMID:17996711, PMID:17996710, PMID:25288561]. It binds branched and D-loop DNA intermediates through two distinct DNA-binding domains, both required for full activity, and stimulates joint-molecule and D-loop formation only when it can simultaneously make direct physical contact with RAD51 [PMID:17996710, PMID:22375013]. Cryo-EM defines the structural basis: RAD51AP1 engages at least three RAD51-binding sites spanning two adjacent RAD51 protomers, stabilizes the RAD51 N-terminal domain and protomer interface, promotes filament nucleation and stabilization, and stimulates strand exchange [PMID:41337480]. It extends these functions to chromatinized templates by binding nucleosome core particles to anchor donor DNA to the filament [PMID:34058198], and CDK2-mediated phosphorylation at S277/S282 modulates its DNA- and nucleosome-binding avidity to ensure dynamic engagement across consecutive HDR steps [PMID:41534830]. Beyond mitotic HR, RAD51AP1 cooperates with the meiotic recombinase DMC1 through a conserved WVPP motif distinct from its RAD51-binding epitope [PMID:21307306, PMID:21903585], and forms a SUMO-SIM-dependent complex with UAF1 that further enhances RAD51-mediated pairing and contributes DNA-binding activity to FANCD2 deubiquitination by USP1-UAF1 [PMID:27239033, PMID:31253762]. At ALT telomeres, RAD51AP1 binds TERRA RNA to assemble R-loops that generate persistent G-quadruplexes, driving an R-to-D-loop switch that enables RAD52-independent break-induced replication and telomere maintenance, a function sustained by MMS21-dependent SUMOylation [PMID:31400850, PMID:36265488, PMID:36265486]. RAD51AP1 also associates with pre-rRNA, which facilitates its recruitment to double-strand breaks and supports phase separation into foci [PMID:38403248].","teleology":[{"year":2007,"claim":"Established RAD51AP1 as a post-synaptic HR factor: the question was where in the recombination pathway it acts, and reconstitution showed it stimulates D-loop/joint-molecule formation after filament assembly via combined structure-specific DNA binding and RAD51 contact.","evidence":"In vitro D-loop and joint-molecule assays with purified protein, EMSA on branched vs linear substrates, RNAi HR assays, XRCC3 epistasis","pmids":["17996711","17996710"],"confidence":"High","gaps":["Did not resolve the structural basis of RAD51 contact","Number and location of RAD51-binding sites unknown"]},{"year":2006,"claim":"Mapped the RAD51-interaction module to a conserved C-terminal motif shared with RAD51AP2, defining the molecular determinant of recombinase binding.","evidence":"Yeast two-hybrid, truncation and point mutagenesis in HEK293, Co-IP","pmids":["16990250"],"confidence":"Medium","gaps":["Functional consequence of motif mutations in HR not assessed here","Single-lab interaction mapping"]},{"year":2011,"claim":"Extended RAD51AP1 function to meiotic recombination by showing it stimulates DMC1 and uses a distinct WVPP epitope, separating its mitotic and meiotic recombinase partnerships.","evidence":"In vitro DMC1 D-loop/synaptic complex assays, Co-IP, WVPP mutagenesis, spermatocyte immunofluorescence","pmids":["21307306","21903585"],"confidence":"High","gaps":["In vivo meiotic requirement not tested via knockout","Structural basis of WVPP-DMC1 contact unknown"]},{"year":2012,"claim":"Defined RAD51AP1 as a bipartite DNA-binding protein, showing two distinct DNA-binding domains are both required for cellular activity.","evidence":"Domain mapping by mutagenesis, EMSA, cellular complementation","pmids":["22375013"],"confidence":"High","gaps":["Distinct biochemical roles of the two domains not separated","No structural model of DNA engagement"]},{"year":2014,"claim":"Connected RAD51AP1 to replication-fork integrity in vertebrate cells and confirmed it acts after RAD51 foci formation by showing impaired foci resolution rather than assembly.","evidence":"DT40 gene inactivation, DNA fiber assay, RAD51 foci kinetics, complementation","pmids":["25288561"],"confidence":"High","gaps":["Mechanism linking HR defect to fork progression not defined","Origin-firing increase mechanism unresolved"]},{"year":2016,"claim":"Identified UAF1 as a stable partner, showing a SUMO-SIM interface builds a RAD51AP1-UAF1-RAD51 complex that enhances pairing and a separable role in regulating a later HR step and protein stability.","evidence":"In vitro synaptic complex/D-loop assays, SUMO-SIM mutagenesis, reciprocal Co-IP, RAD51 foci and stability assays","pmids":["27239033","27463890"],"confidence":"High","gaps":["Relationship between USP1-independent pairing role and USP1-UAF1 deubiquitination role unclear at this stage"]},{"year":2019,"claim":"Demonstrated RAD51AP1's DNA-binding activity feeds into the Fanconi pathway by substituting for UAF1 DNA binding in FANCD2 deubiquitination.","evidence":"Reconstituted USP1-UAF1-RAD51AP1-FANCD2 deubiquitination assay, separation-of-function mutants, cellular assays","pmids":["31253762"],"confidence":"High","gaps":["How DNA binding stimulates the catalytic deubiquitination step mechanistically not resolved"]},{"year":2019,"claim":"Established RAD51AP1 as essential for ALT telomere maintenance and showed its levels are controlled by MMS21-dependent SUMOylation, linking it to RAD52-POLD3 break-induced synthesis.","evidence":"ALT+ cell KO, telomere FISH, cGAS activation, SUMOylation assay, SUMO-site mutagenesis","pmids":["31400850"],"confidence":"High","gaps":["Molecular substrate engaged at ALT telomeres not yet defined here","How SUMOylation alters activity unresolved"]},{"year":2021,"claim":"Showed RAD51AP1 binds nucleosomes, providing a mechanism to anchor chromatinized donor DNA to the RAD51 filament.","evidence":"In vitro NCP/octamer binding, joint-molecule assays with chromatinized DNA, domain mapping","pmids":["34058198"],"confidence":"High","gaps":["In vivo contribution of nucleosome binding to HR not isolated","Histone-contact residues not pinpointed"]},{"year":2022,"claim":"Revealed an RNA-directed function at ALT telomeres: RAD51AP1 binds TERRA to build R-loops that generate G-quadruplexes and drive an R-to-D-loop switch enabling RAD52-independent break-induced replication.","evidence":"In vitro and cellular TERRA R-loop assays, S9.6 quantification, G4 detection, D-loop assays in RAD52 KO, SUMO-SIM mutants, proteomics","pmids":["36265488","36265486"],"confidence":"High","gaps":["How the SUMO-SIM axis switches RAD51AP1 between DNA and RNA functions unresolved","G4-resolution step not defined"]},{"year":2022,"claim":"Defined RAD51AP1 and RAD54L as non-redundant HR sub-pathways downstream of RAD51 through synthetic genotoxic sensitivity.","evidence":"Double KO clonogenic survival with olaparib, MMC, hydroxyurea","pmids":["35652094"],"confidence":"Medium","gaps":["Molecular divergence point between the two sub-pathways not mapped","Single-lab epistasis"]},{"year":2024,"claim":"Identified pre-rRNA as a binding partner that facilitates RAD51AP1 recruitment to DSBs and promotes its phase separation into foci.","evidence":"RIP, DSB colocalization imaging, Pol I inhibition, in vitro phase separation","pmids":["38403248"],"confidence":"Medium","gaps":["Functional necessity of phase separation for HR not established","Single-lab finding"]},{"year":2024,"claim":"Placed RAD51AP1 in a transcriptionally driven drug-resistance circuit, with E2F1/H3K27ac/SOX9 inducing its expression to activate RAD51-UAF1 HR and confer temozolomide resistance in EGFRvIII glioblastoma.","evidence":"CRISPR synthetic-lethal screen, ChIP-seq/PCR, KD/OE HR and drug-sensitivity assays","pmids":["40211735"],"confidence":"Medium","gaps":["Generality beyond EGFRvIII glioblastoma untested","Single-lab"]},{"year":2025,"claim":"Resolved the structural mechanism of RAD51 stimulation: cryo-EM showed RAD51AP1 uses three binding sites across two protomers to stabilize the filament interface and promote nucleation and strand exchange.","evidence":"Cryo-EM of RAD51-ssDNA filaments +/- RAD51AP1 in ATP and ADP states, biochemical strand-exchange and stabilization assays","pmids":["41337480"],"confidence":"High","gaps":["Structure of RAD51AP1 DNA-binding domains on substrate not resolved","Meiotic DMC1 filament structure not addressed"]},{"year":2025,"claim":"Showed CDK2 phosphorylation at S277/S282 tunes RAD51AP1 binding avidity to ensure dynamic, productive cycling across consecutive HDR steps rather than maximal static binding.","evidence":"Phospho-deficient and phosphomimetic mutants, in vitro D-loop/EMSA, cellular toxicity and replication rescue, CDK2 identification","pmids":["41534830"],"confidence":"High","gaps":["Spatiotemporal control of CDK2 phosphorylation during HR not mapped","Phosphatase reversing the mark unknown"]},{"year":null,"claim":"How RAD51AP1 integrates its competing DNA, RNA, nucleosome, and partner interactions into a single regulated switch — and how SUMOylation, phosphorylation, and SUMO-SIM signals are coordinated across mitotic HR, meiosis, and ALT telomere maintenance — remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No unified model coupling RNA-binding and DNA-binding modes","In vivo meiotic and ALT requirements not dissected by domain","Interplay of CDK2 and SUMO regulation undefined"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,1,4,11]},{"term_id":"GO:0003723","term_label":"RNA binding","supporting_discovery_ids":[12,13,15]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,1,16]},{"term_id":"GO:0042393","term_label":"histone binding","supporting_discovery_ids":[11]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[6,8]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[10,15]},{"term_id":"GO:0000228","term_label":"nuclear chromosome","supporting_discovery_ids":[9,12,13]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,1,10,16]},{"term_id":"R-HSA-1474165","term_label":"Reproduction","supporting_discovery_ids":[2,3]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[10]}],"complexes":["RAD51AP1-UAF1 complex","USP1-UAF1-RAD51AP1 complex"],"partners":["RAD51","DMC1","UAF1","USP1","MMS21","CDK2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q96B01","full_name":"RAD51-associated protein 1","aliases":["RAD51-interacting protein"],"length_aa":352,"mass_kda":38.5,"function":"Structure-specific DNA-binding protein involved in DNA repair by promoting RAD51-mediated homologous recombination (PubMed:17996710, PubMed:17996711, PubMed:20871616, PubMed:25288561, PubMed:26323318). Acts by stimulating D-Loop formation by RAD51: specifically enhances joint molecule formation through its structure-specific DNA interaction and its interaction with RAD51 (PubMed:17996710, PubMed:17996711). Binds single-stranded DNA (ssDNA), double-stranded DNA (dsDNA) and secondary DNA structures, such as D-loop structures: has a strong preference for branched-DNA structures that are obligatory intermediates during joint molecule formation (PubMed:17996710, PubMed:17996711, PubMed:22375013, PubMed:9396801). Cooperates with WDR48/UAF1 to stimulate RAD51-mediated homologous recombination: both WDR48/UAF1 and RAD51AP1 have coordinated role in DNA-binding during homologous recombination and DNA repair (PubMed:27239033, PubMed:27463890, PubMed:32350107). WDR48/UAF1 and RAD51AP1 also have a coordinated role in DNA-binding to promote USP1-mediated deubiquitination of FANCD2 (PubMed:31253762). Also involved in meiosis by promoting DMC1-mediated homologous meiotic recombination (PubMed:21307306). Key mediator of alternative lengthening of telomeres (ALT) pathway, a homology-directed repair mechanism of telomere elongation that controls proliferation in aggressive cancers, by stimulating homologous recombination (PubMed:31400850). May also bind RNA; additional evidences are however required to confirm RNA-binding in vivo (PubMed:9396801)","subcellular_location":"Chromosome; Nucleus; Chromosome, telomere","url":"https://www.uniprot.org/uniprotkb/Q96B01/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RAD51AP1","classification":"Not Classified","n_dependent_lines":0,"n_total_lines":1208,"dependency_fraction":0.0},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/RAD51AP1","total_profiled":1310},"omim":[{"mim_id":"615384","title":"SCAFFOLDING PROTEIN INVOLVED IN DNA REPAIR; SPIDR","url":"https://www.omim.org/entry/615384"},{"mim_id":"615383","title":"FIDGETIN-LIKE PROTEIN 1; FIGNL1","url":"https://www.omim.org/entry/615383"},{"mim_id":"603070","title":"RAD51-ASSOCIATED PROTEIN 1; RAD51AP1","url":"https://www.omim.org/entry/603070"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"bone marrow","ntpm":15.9},{"tissue":"lymphoid tissue","ntpm":13.4}],"url":"https://www.proteinatlas.org/search/RAD51AP1"},"hgnc":{"alias_symbol":["PIR51"],"prev_symbol":[]},"alphafold":{"accession":"Q96B01","domains":[],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96B01","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96B01-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96B01-F1-predicted_aligned_error_v6.png","plddt_mean":58.66},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RAD51AP1","jax_strain_url":"https://www.jax.org/strain/search?query=RAD51AP1"},"sequence":{"accession":"Q96B01","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96B01.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96B01/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96B01"}},"corpus_meta":[{"pmid":"17996711","id":"PMC_17996711","title":"Promotion of homologous recombination and genomic stability by RAD51AP1 via RAD51 recombinase 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RAD51AP1 functions at a step subsequent to assembly of the RAD51-ssDNA nucleoprotein filament. RAD51AP1 is epistatic to the HR protein XRCC3.\",\n      \"method\": \"In vitro D-loop assay with purified RAD51AP1, EMSA for DNA binding, RNAi knockdown with HR repair assay and chromosomal break analysis, epistasis analysis with XRCC3\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro D-loop assay with purified protein, mutagenesis, cellular epistasis, replicated in companion paper same year\",\n      \"pmids\": [\"17996711\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2007,\n      \"finding\": \"RAD51AP1 is a structure-specific DNA binding protein with selective affinity for branched-DNA structures (obligatory intermediates during joint molecule formation) and stimulates RAD51-mediated joint molecule formation through the combination of structure-specific DNA binding and direct physical contact with RAD51.\",\n      \"method\": \"In vitro joint molecule formation assay, DNA binding assays (EMSA) with branched vs. linear substrates, Co-IP/physical interaction mapping, cellular DNA damage sensitivity assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro assay, structure-specific binding demonstrated biochemically, replicated by companion paper same year\",\n      \"pmids\": [\"17996710\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"RAD51AP1 physically associates with the meiosis-specific recombinase DMC1 and stimulates the DMC1-mediated D-loop reaction by enhancing DMC1 presynaptic filament capacity to capture duplex-DNA and assemble the synaptic complex. Functional cooperation requires complex formation between DMC1 and RAD51AP1, and distinct epitopes in RAD51AP1 mediate interactions with RAD51 and DMC1. RAD51AP1 foci colocalize with a subset of DMC1 foci in mouse spermatocytes.\",\n      \"method\": \"In vitro D-loop assay with purified DMC1 and RAD51AP1, synaptic complex assembly assay, Co-IP, immunofluorescence in mouse spermatocytes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro D-loop and synaptic complex assays, confirmed by cellular colocalization, multiple orthogonal methods in one study\",\n      \"pmids\": [\"21307306\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2011,\n      \"finding\": \"A highly conserved WVPP motif in RAD51AP1 is critical for DMC1 interaction but dispensable for RAD51 association, demonstrating that RAD51AP1 uses distinct epitopes to interact with RAD51 versus DMC1. This WVPP motif is reminiscent of the FVPP motif in BRCA2 that mediates DMC1 interaction.\",\n      \"method\": \"Series of truncation and point mutations in RAD51AP1 analyzed by Co-IP and interaction assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis with functional interaction mapping, multiple mutants tested, single lab\",\n      \"pmids\": [\"21903585\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"RAD51AP1 harbors two distinct DNA binding domains that are both required for maximal protein activity under physiological conditions; mutant variants impaired in either or both DNA binding domains are non-functional in cells.\",\n      \"method\": \"Domain mapping by truncation and point mutagenesis, EMSA, cellular complementation assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis, in vitro DNA binding, and cellular functional assays, multiple orthogonal methods in one study\",\n      \"pmids\": [\"22375013\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"RAD51AP1/PIR51 and RAD51AP2 use the same conserved C-terminal structural motif (~57 residues in RAD51AP2, mapped to 40 aa in RAD51AP1) for RAD51 binding. Point mutations in this motif abolish RAD51 interaction.\",\n      \"method\": \"Yeast two-hybrid, truncation and point mutation analysis in HEK293 cells, Co-IP\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction mapping using multiple truncations and point mutants, two-hybrid plus cellular Co-IP, single lab\",\n      \"pmids\": [\"16990250\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"UAF1 binds DNA and forms a dimeric complex with RAD51AP1 through SUMO-like domains in UAF1 and a SUMO-interacting motif (SIM) in RAD51AP1, and a trimeric complex with RAD51 through RAD51AP1. The RAD51AP1-UAF1 complex cooperates with RAD51 to assemble the synaptic complex and enhances RAD51-mediated homologous DNA pairing in a manner dependent on RAD51AP1 but independent of USP1.\",\n      \"method\": \"In vitro D-loop/synaptic complex assay with purified proteins, Co-IP, domain interaction mapping with SUMO-SIM mutations, cellular HR assay\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro synaptic complex and D-loop assays, biochemical interaction mapping, cellular validation, multiple orthogonal methods\",\n      \"pmids\": [\"27239033\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2016,\n      \"finding\": \"USP1-UAF1 complex interacts with RAD51AP1 via UAF1, which mediates the interaction; depletion of USP1 or UAF1 reduces RAD51AP1 stability. A UAF1 interaction-deficient mutant of RAD51AP1 causes persistent RAD51 foci following DNA damage, indicating RAD51AP1-UAF1 regulates a later step in HR repair.\",\n      \"method\": \"Proteomic pulldown of UAF1-interacting proteins, Co-IP, protein stability assays, RAD51 foci analysis after DNA damage, chromosomal aberration assay\",\n      \"journal\": \"Cell cycle (Georgetown, Tex.)\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal Co-IP, mutant complementation with phenotypic readout, single lab with multiple methods\",\n      \"pmids\": [\"27463890\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Efficient FANCD2 deubiquitination by the USP1-UAF1 complex requires DNA and DNA binding by UAF1. The DNA binding activity of UAF1-associated RAD51AP1 can substitute for that of UAF1 in FANCD2 deubiquitination in a reconstituted biochemical system. DNA binding by UAF1 and RAD51AP1 is important for FANCD2 deubiquitination in cells.\",\n      \"method\": \"Reconstituted biochemical deubiquitination assay with purified USP1-UAF1-RAD51AP1 and FANCD2, cellular deubiquitination assay with separation-of-function mutants\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted biochemical system, separation-of-function mutants, cellular validation, multiple orthogonal methods in one study\",\n      \"pmids\": [\"31253762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"RAD51AP1 is required for both RAD51-dependent HR and RAD52-POLD3-dependent break-induced DNA synthesis at ALT telomeres. RAD51AP1 KO in ALT+ cells causes generational telomere shortening, telomere dysfunction, and cytosolic telomeric DNA that activates cGAS. RAD51AP1 protein levels are elevated in ALT+ cells due to MMS21-associated SUMOylation; mutation of a single SUMO-targeted lysine residue perturbs telomere dynamics.\",\n      \"method\": \"RAD51AP1 KO in ALT+ cancer cells, telomere FISH, cGAS activation assay, autophagy assays, SUMOylation assay with MMS21, SUMO-site mutagenesis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO with multiple phenotypic readouts, SUMOylation biochemistry, site-specific mutagenesis with functional consequence, multiple orthogonal methods\",\n      \"pmids\": [\"31400850\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"RAD51AP1 deficiency in vertebrate cells impairs DNA replication fork progression and causes increased replication origin firing. In RAD51AP1-deficient cells, resolution of DNA damage-induced RAD51 foci is greatly slowed while their formation is not impaired, placing RAD51AP1 function after RAD51 filament assembly.\",\n      \"method\": \"Targeted RAD51AP1 gene inactivation in chicken DT40 cells, DNA fiber assay for replication fork speed, RAD51 foci kinetics by immunofluorescence, complementation with human/chicken RAD51AP1\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — genetic KO model, DNA fiber assay, RAD51 foci kinetics, complementation assays, multiple orthogonal methods\",\n      \"pmids\": [\"25288561\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RAD51AP1 binds to nucleosome core particles (NCPs) through a C-terminal region including its DNA-binding domain, and can promote duplex DNA capture and joint-molecule formation with chromatinized template DNA in vitro, suggesting RAD51AP1 anchors the DNA template through nucleosome affinity to the RAD51-ssDNA filament.\",\n      \"method\": \"In vitro binding assays (EMSA, pulldown) with purified NCPs and histone octamers, in vitro D-loop/joint molecule assay with chromatinized DNA, domain mapping by truncation\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — reconstituted in vitro assays with purified NCPs and chromatinized substrates, domain mapping, multiple biochemical methods, single lab\",\n      \"pmids\": [\"34058198\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAD51AP1 interacts with TERRA RNA and uses it to generate D-loop and R-loop HR intermediates at telomeres. RAD51AP1 depletion reduces R-loop formation at telomere DNA breaks. RAD51AP1-mediated TERRA R-loop homeostasis suppresses TERRA transcription and prevents transcription-replication collisions during ALT-HDR. Both TERRA binding and this chromatin-directed function require RAD51AP1's intrinsic SUMO-SIM regulatory axis.\",\n      \"method\": \"TERRA R-loop assays in vitro and at telomeres, RAD51AP1 KD with R-loop measurement (S9.6 antibody), proteomics of RAD51AP1-associated proteins, SUMO-SIM mutant analysis\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (in vitro, cellular, proteomic), genetic KD with specific mechanistic readout, SUMO-SIM mutagenesis, two companion papers simultaneously\",\n      \"pmids\": [\"36265488\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"TERRA forms R-loops in vitro and at telomeres in a RAD51AP1-dependent manner. RAD51AP1-assembled TERRA R-loops generate G-quadruplexes (G4s) at telomeres, which persist after R-loop resolution and enable D-loop formation without RAD52, orchestrating an R-to-D-loop switch that promotes break-induced replication in the RAD52-independent ALT pathway.\",\n      \"method\": \"In vitro R-loop formation assay with purified TERRA and RAD51AP1, telomeric R-loop quantification in RAD51AP1-dependent knockdown cells, G4 detection, D-loop assay in RAD52 KO cells\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — reconstituted in vitro assays, cellular validation in RAD52 KO background, G4 epistasis experiments, multiple orthogonal methods\",\n      \"pmids\": [\"36265486\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RAD51AP1 and RAD54L define two distinct sub-pathways downstream of RAD51 in HR; simultaneous deletion of RAD51AP1 and RAD54L shows synthetic sensitivity to PARP inhibitor (olaparib), mitomycin C, and hydroxyurea, establishing that the two proteins underpin non-redundant HR routes.\",\n      \"method\": \"Double KO of RAD51AP1 and RAD54L in human cancer cell lines, clonogenic survival with olaparib, MMC, hydroxyurea; comparison with RAD54B single KO\",\n      \"journal\": \"Frontiers in cell and developmental biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis via double KO, multiple genotoxic agents, single lab\",\n      \"pmids\": [\"35652094\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"RAD51AP1 associates with pre-rRNA through both its N-terminus and C-terminus. Pre-rRNA colocalizes with RAD51AP1 at double-strand breaks and facilitates RAD51AP1 recruitment to DSBs. RAD51AP1 forms liquid-liquid phase separation in the presence of pre-rRNA in vitro, which may underlie RAD51AP1 foci formation.\",\n      \"method\": \"RNA immunoprecipitation, colocalization at DSBs by imaging, RNA polymerase I inhibitor treatment, in vitro phase separation assay with purified RAD51AP1 and pre-rRNA\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — RIP, cellular colocalization, pharmacological inhibition, in vitro phase separation; single lab, multiple orthogonal methods\",\n      \"pmids\": [\"38403248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAD51AP1 possesses at least three RAD51-binding sites that span two adjacent RAD51 molecules. RAD51AP1 stabilizes the RAD51 N-terminal domain and protomer interface in filaments, promotes RAD51-ssDNA filament nucleation and stabilization, and stimulates strand exchange. Structural data show RAD51AP1 binding induces conformational changes promoting RAD51 DNA association and oligomerization. RAD51-ssDNA filaments expand upon ATP hydrolysis to ADP, explaining reduced RAD51-DNA binding in the ADP state.\",\n      \"method\": \"Cryo-EM structures of RAD51-ssDNA filaments with and without RAD51AP1 in Mg2+-ATP and Mg2+-ADP states, biochemical strand exchange assays, filament stabilization assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structural biology combined with biochemical reconstitution and strand exchange assays, multiple orthogonal methods\",\n      \"pmids\": [\"41337480\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAD51AP1 activity in HDR is regulated by CDK2-mediated phosphorylation at S277 and S282. A phospho-deficient S277/282A mutant more avidly binds ssDNA, dsDNA, and nucleosome core particles and is more proficient in D-loop stimulation in vitro, but fails to rescue RAD51AP1 deficiency in cellular toxicity and DNA replication assays. A phosphomimetic S277/282D mutant fully rescues RAD51AP1 deficiency in cells, suggesting phosphorylation ensures dynamic RAD51AP1 engagement across consecutive HDR steps.\",\n      \"method\": \"Site-directed mutagenesis (S277A, S282A, S277/282D), in vitro D-loop assay, EMSA with ssDNA/dsDNA/NCP, cellular toxicity and DNA replication assays, CDK2 phosphorylation identification\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — mutagenesis combined with in vitro biochemistry, EMSA, and cellular complementation assays; CDK2 identified as the writer; multiple orthogonal methods in one study\",\n      \"pmids\": [\"41534830\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"RAD51AP1 is required for TERRA R-loop formation in telomerase-expressing cells; both RAD51 and RAD51AP1 contribute non-redundant functions to TERRA R-loop formation. TERRA R-loops interfere with semiconservative DNA replication and promote break-induced replication for telomere maintenance.\",\n      \"method\": \"TERRA overexpression in telomerase+ cells, RAD51AP1 depletion, R-loop measurement, DNA replication interference assay, BIR assay\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic depletion with specific R-loop and BIR readouts, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.01.09.632133\"],\n      \"is_preprint\": true\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"E2F1 transcription factor drives RAD51AP1 expression in EGFRvIII-positive glioblastoma cells in response to TMZ treatment; RAD51AP1 promotes formation of the RAD51-UAF1 complex to activate homologous recombination and thereby confers TMZ resistance. H3K27ac and SOX9 together induce RAD51AP1 transcription in EGFRvIII cells.\",\n      \"method\": \"CRISPR/Cas9 synthetic lethal screen, ChIP-seq and ChIP-PCR for H3K27ac and SOX9 at RAD51AP1 promoter, RAD51AP1 KD and OE with HR and drug sensitivity assays\",\n      \"journal\": \"Chinese medical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — CRISPR screen plus ChIP-seq/PCR validation and functional assays; single lab, multiple methods\",\n      \"pmids\": [\"40211735\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RAD51AP1 is a multifunctional RAD51 accessory protein that binds branched/D-loop DNA structures and RNA (including TERRA and pre-rRNA) through two distinct DNA-binding domains, directly interacts with RAD51 via at least three binding sites spanning two adjacent RAD51 protomers to stabilize RAD51-ssDNA filaments and promote filament nucleation, synaptic complex assembly, and strand exchange; it also physically interacts with the meiotic recombinase DMC1 via a distinct WVPP motif to stimulate meiotic recombination; forms a complex with UAF1 (via a SUMO-SIM interface) that further enhances RAD51-mediated DNA pairing and participates in FANCD2 deubiquitination by the USP1-UAF1 complex; binds nucleosome core particles to promote HR on chromatinized templates; assembles TERRA-containing R-loops at ALT telomeres to generate G-quadruplexes and drive an R-to-D-loop switch enabling RAD52-independent break-induced replication; is SUMOylated by MMS21 at ALT+ cells to sustain telomere length; and is regulated by CDK2-mediated phosphorylation at S277/S282 that ensures dynamic engagement across consecutive HDR steps.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RAD51AP1 is a structure-specific DNA-binding accessory factor that promotes RAD51-mediated homologous recombination (HR) at a step downstream of presynaptic filament assembly [#0, #1, #10]. It binds branched and D-loop DNA intermediates through two distinct DNA-binding domains, both required for full activity, and stimulates joint-molecule and D-loop formation only when it can simultaneously make direct physical contact with RAD51 [#1, #4]. Cryo-EM defines the structural basis: RAD51AP1 engages at least three RAD51-binding sites spanning two adjacent RAD51 protomers, stabilizes the RAD51 N-terminal domain and protomer interface, promotes filament nucleation and stabilization, and stimulates strand exchange [#16]. It extends these functions to chromatinized templates by binding nucleosome core particles to anchor donor DNA to the filament [#11], and CDK2-mediated phosphorylation at S277/S282 modulates its DNA- and nucleosome-binding avidity to ensure dynamic engagement across consecutive HDR steps [#17]. Beyond mitotic HR, RAD51AP1 cooperates with the meiotic recombinase DMC1 through a conserved WVPP motif distinct from its RAD51-binding epitope [#2, #3], and forms a SUMO-SIM-dependent complex with UAF1 that further enhances RAD51-mediated pairing and contributes DNA-binding activity to FANCD2 deubiquitination by USP1-UAF1 [#6, #8]. At ALT telomeres, RAD51AP1 binds TERRA RNA to assemble R-loops that generate persistent G-quadruplexes, driving an R-to-D-loop switch that enables RAD52-independent break-induced replication and telomere maintenance, a function sustained by MMS21-dependent SUMOylation [#9, #12, #13]. RAD51AP1 also associates with pre-rRNA, which facilitates its recruitment to double-strand breaks and supports phase separation into foci [#15].\",\n  \"teleology\": [\n    {\n      \"year\": 2007,\n      \"claim\": \"Established RAD51AP1 as a post-synaptic HR factor: the question was where in the recombination pathway it acts, and reconstitution showed it stimulates D-loop/joint-molecule formation after filament assembly via combined structure-specific DNA binding and RAD51 contact.\",\n      \"evidence\": \"In vitro D-loop and joint-molecule assays with purified protein, EMSA on branched vs linear substrates, RNAi HR assays, XRCC3 epistasis\",\n      \"pmids\": [\"17996711\", \"17996710\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve the structural basis of RAD51 contact\", \"Number and location of RAD51-binding sites unknown\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Mapped the RAD51-interaction module to a conserved C-terminal motif shared with RAD51AP2, defining the molecular determinant of recombinase binding.\",\n      \"evidence\": \"Yeast two-hybrid, truncation and point mutagenesis in HEK293, Co-IP\",\n      \"pmids\": [\"16990250\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional consequence of motif mutations in HR not assessed here\", \"Single-lab interaction mapping\"]\n    },\n    {\n      \"year\": 2011,\n      \"claim\": \"Extended RAD51AP1 function to meiotic recombination by showing it stimulates DMC1 and uses a distinct WVPP epitope, separating its mitotic and meiotic recombinase partnerships.\",\n      \"evidence\": \"In vitro DMC1 D-loop/synaptic complex assays, Co-IP, WVPP mutagenesis, spermatocyte immunofluorescence\",\n      \"pmids\": [\"21307306\", \"21903585\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo meiotic requirement not tested via knockout\", \"Structural basis of WVPP-DMC1 contact unknown\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Defined RAD51AP1 as a bipartite DNA-binding protein, showing two distinct DNA-binding domains are both required for cellular activity.\",\n      \"evidence\": \"Domain mapping by mutagenesis, EMSA, cellular complementation\",\n      \"pmids\": [\"22375013\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Distinct biochemical roles of the two domains not separated\", \"No structural model of DNA engagement\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected RAD51AP1 to replication-fork integrity in vertebrate cells and confirmed it acts after RAD51 foci formation by showing impaired foci resolution rather than assembly.\",\n      \"evidence\": \"DT40 gene inactivation, DNA fiber assay, RAD51 foci kinetics, complementation\",\n      \"pmids\": [\"25288561\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism linking HR defect to fork progression not defined\", \"Origin-firing increase mechanism unresolved\"]\n    },\n    {\n      \"year\": 2016,\n      \"claim\": \"Identified UAF1 as a stable partner, showing a SUMO-SIM interface builds a RAD51AP1-UAF1-RAD51 complex that enhances pairing and a separable role in regulating a later HR step and protein stability.\",\n      \"evidence\": \"In vitro synaptic complex/D-loop assays, SUMO-SIM mutagenesis, reciprocal Co-IP, RAD51 foci and stability assays\",\n      \"pmids\": [\"27239033\", \"27463890\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Relationship between USP1-independent pairing role and USP1-UAF1 deubiquitination role unclear at this stage\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Demonstrated RAD51AP1's DNA-binding activity feeds into the Fanconi pathway by substituting for UAF1 DNA binding in FANCD2 deubiquitination.\",\n      \"evidence\": \"Reconstituted USP1-UAF1-RAD51AP1-FANCD2 deubiquitination assay, separation-of-function mutants, cellular assays\",\n      \"pmids\": [\"31253762\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How DNA binding stimulates the catalytic deubiquitination step mechanistically not resolved\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Established RAD51AP1 as essential for ALT telomere maintenance and showed its levels are controlled by MMS21-dependent SUMOylation, linking it to RAD52-POLD3 break-induced synthesis.\",\n      \"evidence\": \"ALT+ cell KO, telomere FISH, cGAS activation, SUMOylation assay, SUMO-site mutagenesis\",\n      \"pmids\": [\"31400850\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Molecular substrate engaged at ALT telomeres not yet defined here\", \"How SUMOylation alters activity unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Showed RAD51AP1 binds nucleosomes, providing a mechanism to anchor chromatinized donor DNA to the RAD51 filament.\",\n      \"evidence\": \"In vitro NCP/octamer binding, joint-molecule assays with chromatinized DNA, domain mapping\",\n      \"pmids\": [\"34058198\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"In vivo contribution of nucleosome binding to HR not isolated\", \"Histone-contact residues not pinpointed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Revealed an RNA-directed function at ALT telomeres: RAD51AP1 binds TERRA to build R-loops that generate G-quadruplexes and drive an R-to-D-loop switch enabling RAD52-independent break-induced replication.\",\n      \"evidence\": \"In vitro and cellular TERRA R-loop assays, S9.6 quantification, G4 detection, D-loop assays in RAD52 KO, SUMO-SIM mutants, proteomics\",\n      \"pmids\": [\"36265488\", \"36265486\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"How the SUMO-SIM axis switches RAD51AP1 between DNA and RNA functions unresolved\", \"G4-resolution step not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined RAD51AP1 and RAD54L as non-redundant HR sub-pathways downstream of RAD51 through synthetic genotoxic sensitivity.\",\n      \"evidence\": \"Double KO clonogenic survival with olaparib, MMC, hydroxyurea\",\n      \"pmids\": [\"35652094\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular divergence point between the two sub-pathways not mapped\", \"Single-lab epistasis\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Identified pre-rRNA as a binding partner that facilitates RAD51AP1 recruitment to DSBs and promotes its phase separation into foci.\",\n      \"evidence\": \"RIP, DSB colocalization imaging, Pol I inhibition, in vitro phase separation\",\n      \"pmids\": [\"38403248\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Functional necessity of phase separation for HR not established\", \"Single-lab finding\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Placed RAD51AP1 in a transcriptionally driven drug-resistance circuit, with E2F1/H3K27ac/SOX9 inducing its expression to activate RAD51-UAF1 HR and confer temozolomide resistance in EGFRvIII glioblastoma.\",\n      \"evidence\": \"CRISPR synthetic-lethal screen, ChIP-seq/PCR, KD/OE HR and drug-sensitivity assays\",\n      \"pmids\": [\"40211735\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Generality beyond EGFRvIII glioblastoma untested\", \"Single-lab\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Resolved the structural mechanism of RAD51 stimulation: cryo-EM showed RAD51AP1 uses three binding sites across two protomers to stabilize the filament interface and promote nucleation and strand exchange.\",\n      \"evidence\": \"Cryo-EM of RAD51-ssDNA filaments +/- RAD51AP1 in ATP and ADP states, biochemical strand-exchange and stabilization assays\",\n      \"pmids\": [\"41337480\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structure of RAD51AP1 DNA-binding domains on substrate not resolved\", \"Meiotic DMC1 filament structure not addressed\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Showed CDK2 phosphorylation at S277/S282 tunes RAD51AP1 binding avidity to ensure dynamic, productive cycling across consecutive HDR steps rather than maximal static binding.\",\n      \"evidence\": \"Phospho-deficient and phosphomimetic mutants, in vitro D-loop/EMSA, cellular toxicity and replication rescue, CDK2 identification\",\n      \"pmids\": [\"41534830\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Spatiotemporal control of CDK2 phosphorylation during HR not mapped\", \"Phosphatase reversing the mark unknown\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RAD51AP1 integrates its competing DNA, RNA, nucleosome, and partner interactions into a single regulated switch — and how SUMOylation, phosphorylation, and SUMO-SIM signals are coordinated across mitotic HR, meiosis, and ALT telomere maintenance — remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No unified model coupling RNA-binding and DNA-binding modes\", \"In vivo meiotic and ALT requirements not dissected by domain\", \"Interplay of CDK2 and SUMO regulation undefined\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1, 4, 11]},\n      {\"term_id\": \"GO:0003723\", \"supporting_discovery_ids\": [12, 13, 15]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 1, 16]},\n      {\"term_id\": \"GO:0042393\", \"supporting_discovery_ids\": [11]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [6, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [10, 15]},\n      {\"term_id\": \"GO:0000228\", \"supporting_discovery_ids\": [9, 12, 13]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 1, 10, 16]},\n      {\"term_id\": \"R-HSA-1474165\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [10]}\n    ],\n    \"complexes\": [\n      \"RAD51AP1-UAF1 complex\",\n      \"USP1-UAF1-RAD51AP1 complex\"\n    ],\n    \"partners\": [\n      \"RAD51\",\n      \"DMC1\",\n      \"UAF1\",\n      \"USP1\",\n      \"MMS21\",\n      \"CDK2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":7,"faith_total":7,"faith_pct":100.0}}