{"gene":"RADX","run_date":"2026-06-10T06:43:36","timeline":{"discoveries":[{"year":2017,"finding":"RADX was identified as an RPA-like, single-strand DNA (ssDNA) binding protein that is recruited to replication forks, where it antagonizes RAD51 to prevent fork collapse. Inactivation of RADX causes excessive RAD51 activity, leading to slowed replication elongation and double-strand breaks.","method":"Proteomic identification at replication forks, genetic depletion (siRNA/CRISPR), DNA fiber assays, γH2AX foci","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 2 / Strong — reciprocal functional assays, multiple orthogonal methods (iPOND mass spec, fiber assays, DSB detection), replicated across multiple subsequent studies","pmids":["28735897"],"is_preprint":false},{"year":2017,"finding":"RADX binds ssDNA via an N-terminal OB fold cluster, which mediates its recruitment to sites of replication stress. Disruption of RADX expression or ssDNA binding leads to enhanced replication fork stalling and degradation. A balanced interplay between RADX and RPA ssDNA-binding activities is critical for replication integrity.","method":"Biochemical ssDNA binding assays, OB-fold deletion/mutation analysis, immunofluorescence at replication stress sites, DNA fiber assays","journal":"EMBO reports","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — in vitro ssDNA binding with domain mapping, cellular localization with functional consequence, two orthogonal methods in one study","pmids":["29021206"],"is_preprint":false},{"year":2018,"finding":"RADX antagonizes RAD51 at stalled replication forks by competing with RAD51 for binding to ssDNA. Silencing RADX restores fork protection in cells deficient for BRCA1, BRCA2, FANCA, FANCD2, or BOD1L. RADX overexpression causes fork degradation dependent on MRE11 and DNA2 nucleases and requires fork reversal. The level of RAD51 determines fork fate, with more RAD51 required for protection than reversal.","method":"DNA fiber assays, siRNA knockdown in multiple BRCA/Fanconi pathway-deficient cell lines, RADX overexpression, nuclease inhibitor experiments","journal":"Cell reports","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple genetic backgrounds tested, multiple orthogonal methods, functional competition between RADX and RAD51 for ssDNA demonstrated biochemically","pmids":["30021152"],"is_preprint":false},{"year":2020,"finding":"RADX condenses ssDNA filaments even when coated with RPA at physiological protein ratios, forming higher-order assemblies that can capture ssDNA in trans. RADX blocks RPA displacement by RAD51 and prevents RAD51 loading onto ssDNA, acting as an ssDNA condensation protein.","method":"Single-molecule imaging (total internal reflection fluorescence microscopy), in vitro reconstitution with purified proteins, single-molecule curtains","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — single-molecule in vitro reconstitution with purified proteins, direct visualization of RADX condensation and RAD51 loading inhibition, multiple imaging conditions","pmids":["32621611"],"is_preprint":false},{"year":2021,"finding":"RADX directly inhibits RAD51 strand exchange and D-loop formation. RADX selectively interacts with ATP-bound RAD51, stimulates RAD51 ATP hydrolysis, and destabilizes RAD51 nucleofilaments. Both ssDNA binding and direct RAD51 interaction are required for RADX to maintain replication fork elongation rates. BRCA2 can overcome RADX-dependent RAD51 inhibition, establishing RADX and BRCA2 as opposing regulators of RAD51 nucleofilament stability.","method":"In vitro strand exchange assay, D-loop assay, ATPase assay, biochemical interaction studies with ATP-bound RAD51, genetic complementation with BRCA2, DNA fiber assays","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1 / Strong — multiple in vitro biochemical assays (strand exchange, ATPase, D-loop), mutagenesis, epistasis with BRCA2, replicated across two orthogonal method classes","pmids":["33453169"],"is_preprint":false},{"year":2021,"finding":"RADX can either inhibit or promote fork reversal depending on replication stress levels: it inhibits fork reversal at elongating forks to prevent collapse, but at persistently stalled forks, RADX localizes to promote reversed fork structure formation. RADX increases SMARCAL1-dependent fork reversal when pre-bound RAD51 is inhibitory, acting via direct interaction with both RAD51 and ssDNA.","method":"DNA fiber assays, electron microscopy of replication intermediates, genetic epistasis with RTEL1 and fork protection factors, in vitro fork reversal assay with SMARCAL1 and RADX","journal":"Molecular cell","confidence":"High","confidence_rationale":"Tier 1-2 / Strong — EM visualization of fork structures, in vitro reconstitution with SMARCAL1, genetic epistasis with RTEL1 and fork protection factors, multiple orthogonal methods","pmids":["34107305"],"is_preprint":false},{"year":2022,"finding":"RADX functions as a homo-oligomer to regulate replication fork stability. RADX oligomerizes via at least two interaction surfaces, including a C-terminal region. Mutations preventing oligomerization abolish RADX function in cells, and this can be rescued by addition of a heterologous dimerization domain.","method":"Biochemical oligomerization assays, mutagenesis of oligomerization surfaces, complementation with heterologous dimerization domain, DNA fiber assays in cells","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — biochemical oligomerization mapping with mutagenesis, functional rescue experiments in cells, two orthogonal methods","pmids":["35120927"],"is_preprint":false},{"year":2023,"finding":"CRISPR base editing screen identified RADX separation-of-function mutants that bind DNA and RAD51 but have reduced ability to stimulate RAD51 ATP hydrolysis. Cells expressing these mutants accumulate RAD51 on chromatin, exhibit replication defects, accumulate DNA damage, and are hypersensitive to replication stress, indicating that RADX must promote RAD51 ATP turnover to regulate genome stability during DNA replication.","method":"CRISPR base editing screen, ATPase assay, chromatin fractionation, DNA fiber assay, DNA damage sensitivity assays","journal":"Journal of molecular biology","confidence":"High","confidence_rationale":"Tier 1-2 / Moderate — base editing screen with functional follow-up, in vitro ATPase validation of separation-of-function mutants, multiple cellular readouts","pmids":["37572935"],"is_preprint":false},{"year":2024,"finding":"Cryo-EM structure of RADX (no structurally characterized orthologs) determined ab initio at 2–4 Å resolution. RADX forms concentration-dependent oligomeric states (predominantly trimers in the presence of ssDNA). The structure reveals the molecular basis for oligomerization and multivalent ssDNA binding. Negative stain EM imaging shows a RADX oligomer at the end of RAD51 filaments, supporting a model in which RADX caps and restricts RAD51 filament ends.","method":"Cryo-EM structure determination, mass photometry (oligomeric state analysis), negative stain EM of RADX-RAD51 filament complexes","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Moderate — high-resolution cryo-EM structure with functional validation by negative stain EM of RADX-RAD51 complexes, mass photometry, multiple orthogonal structural methods in one study","pmids":["38466836"],"is_preprint":false}],"current_model":"RADX is an RPA-like ssDNA-binding protein that forms homo-oligomers (predominantly trimers) via OB fold domains, binds ssDNA multivalently, and directly interacts with ATP-bound RAD51 at replication forks to stimulate its ATPase activity, destabilize RAD51 nucleofilaments, and block RAD51-mediated strand exchange — thereby counteracting BRCA2 to confine fork reversal to persistently stalled forks, prevent excessive fork slowing, and maintain genome stability."},"narrative":{"mechanistic_narrative":"RADX is an RPA-like single-stranded DNA (ssDNA)-binding protein that operates at replication forks to restrain RAD51 activity and thereby preserve genome stability [PMID:28735897]. It binds ssDNA through an N-terminal OB-fold cluster that mediates its recruitment to sites of replication stress, and its activity is balanced against that of RPA to maintain replication integrity [PMID:29021206]. RADX antagonizes RAD51 by two cooperating mechanisms: it competes with RAD51 for ssDNA and condenses RPA-coated ssDNA into higher-order assemblies that block RPA displacement and prevent RAD51 loading [PMID:30021152, PMID:32621611], and it directly engages ATP-bound RAD51 to stimulate RAD51 ATP hydrolysis, destabilize RAD51 nucleofilaments, and inhibit strand exchange and D-loop formation — an activity that BRCA2 can override, establishing RADX and BRCA2 as opposing regulators of filament stability [PMID:33453169, PMID:37572935]. Through this regulation RADX confines fork reversal: it suppresses reversal at elongating forks to prevent collapse but promotes SMARCAL1-dependent reversal at persistently stalled forks when pre-bound RAD51 is inhibitory [PMID:34107305]. RADX functions as a homo-oligomer — predominantly a trimer on ssDNA — assembled via multiple interaction surfaces including a C-terminal region, and structural analysis indicates it caps and restricts RAD51 filament ends [PMID:35120927, PMID:38466836].","teleology":[{"year":2017,"claim":"Established RADX as a previously uncharacterized fork-associated ssDNA-binding factor whose loss destabilizes replication, framing it as a RAD51 antagonist rather than a generic fork protein.","evidence":"Proteomic identification at forks with siRNA/CRISPR depletion, DNA fiber assays, and γH2AX foci","pmids":["28735897"],"confidence":"High","gaps":["Did not resolve whether antagonism is via ssDNA competition or direct RAD51 binding","No structural or biochemical mechanism for fork recruitment"]},{"year":2017,"claim":"Mapped the ssDNA-binding determinant to an N-terminal OB-fold cluster and tied that binding to stress-site recruitment, defining the biochemical basis of RADX localization.","evidence":"In vitro ssDNA binding with OB-fold deletion/mutation, immunofluorescence, and DNA fiber assays","pmids":["29021206"],"confidence":"High","gaps":["Did not establish how RADX-RPA balance is set quantitatively","Did not test direct RAD51 contact"]},{"year":2018,"claim":"Showed RADX competes with RAD51 for ssDNA and that RAD51 dosage dictates fork fate, explaining why RADX loss rescues fork protection in BRCA/Fanconi-deficient cells.","evidence":"DNA fiber assays across multiple BRCA/Fanconi-deficient lines, overexpression, and nuclease-inhibitor experiments","pmids":["30021152"],"confidence":"High","gaps":["Competition demonstrated functionally but not at single-molecule resolution","Direct RADX-RAD51 protein interaction not yet shown"]},{"year":2020,"claim":"Resolved the ssDNA-level mechanism by showing RADX condenses even RPA-coated ssDNA and blocks RPA displacement, recasting RADX as an ssDNA condensation protein that prevents RAD51 loading.","evidence":"Single-molecule TIRF imaging and ssDNA curtains with purified proteins","pmids":["32621611"],"confidence":"High","gaps":["Did not address whether RADX also acts on assembled RAD51 filaments","In vitro ratios may not capture in vivo regulation"]},{"year":2021,"claim":"Identified a second, direct mechanism: RADX binds ATP-bound RAD51, stimulates its ATPase, destabilizes nucleofilaments and blocks strand exchange, and placed RADX opposite BRCA2 in RAD51 filament regulation.","evidence":"In vitro strand exchange, D-loop and ATPase assays, ATP-state-selective interaction studies, and BRCA2 epistasis with fiber assays","pmids":["33453169"],"confidence":"High","gaps":["Structural basis of the ATP-bound-RAD51 interaction not defined","Quantitative interplay with the ssDNA-condensation activity unresolved"]},{"year":2021,"claim":"Reconciled RADX's apparently opposing roles by showing it inhibits reversal at elongating forks but promotes SMARCAL1-dependent reversal at persistently stalled forks, making fork outcome stress-dependent.","evidence":"DNA fiber assays, electron microscopy of replication intermediates, RTEL1 epistasis, and in vitro SMARCAL1 fork reversal reconstitution","pmids":["34107305"],"confidence":"High","gaps":["Signal that switches RADX between inhibitory and promoting modes is unknown","Threshold defining 'persistent' stalling not defined"]},{"year":2022,"claim":"Demonstrated that homo-oligomerization, via multiple surfaces including a C-terminal region, is obligatory for RADX function in cells.","evidence":"Oligomerization mapping with mutagenesis, heterologous dimerization-domain rescue, and DNA fiber assays","pmids":["35120927"],"confidence":"High","gaps":["Oligomeric stoichiometry on ssDNA not yet defined","Did not resolve oligomer architecture structurally"]},{"year":2023,"claim":"Used separation-of-function mutants to prove that RADX must actively promote RAD51 ATP turnover — not merely bind DNA and RAD51 — to maintain genome stability.","evidence":"CRISPR base-editing screen with ATPase, chromatin fractionation, fiber, and damage-sensitivity assays","pmids":["37572935"],"confidence":"High","gaps":["Atomic mechanism by which RADX stimulates RAD51 ATPase not defined","Did not separate ssDNA-condensation from ATPase-stimulation contributions in vivo"]},{"year":2024,"claim":"Provided the first RADX structure, defining oligomerization and multivalent ssDNA binding and visualizing RADX capping RAD51 filament ends, giving a physical model for filament restriction.","evidence":"Ab initio cryo-EM at 2–4 Å, mass photometry, and negative-stain EM of RADX-RAD51 filament complexes","pmids":["38466836"],"confidence":"High","gaps":["No high-resolution structure of the RADX-RAD51 interface","Capping model not yet tested with structure-guided interface mutants in cells"]},{"year":null,"claim":"How the two RADX activities (ssDNA condensation versus direct RAD51 ATPase stimulation/filament capping) are coordinated and toggled by replication-stress signals to choose fork elongation versus reversal remains unresolved.","evidence":"","pmids":[],"confidence":"High","gaps":["No mechanism for sensing 'persistent' stalling","No structure of the RADX-RAD51 complex interface","Upstream regulation/post-translational control of RADX unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,1,2,3,4]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[2,4,5,7]},{"term_id":"GO:0140313","term_label":"molecular sequestering activity","supporting_discovery_ids":[2,3]}],"localization":[],"pathway":[{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[0,1,2,5]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,4,5]}],"complexes":[],"partners":["RAD51","RPA","BRCA2","SMARCAL1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q6NSI4","full_name":"RPA-related protein RADX","aliases":["RPA-related and RAD51-antagonist, X-chromosome"],"length_aa":855,"mass_kda":97.6,"function":"Single-stranded DNA-binding protein recruited to replication forks to maintain genome stability (PubMed:28735897). Prevents fork collapse by antagonizing the accumulation of RAD51 at forks to ensure the proper balance of fork remodeling and protection without interfering with the capacity of cells to complete homologous recombination of double-strand breaks (PubMed:28735897)","subcellular_location":"Chromosome","url":"https://www.uniprot.org/uniprotkb/Q6NSI4/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/RADX","classification":"Not Classified","n_dependent_lines":1,"n_total_lines":1208,"dependency_fraction":0.0008278145695364238},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"DNAJC7","stoichiometry":0.2},{"gene":"FKBP5","stoichiometry":0.2},{"gene":"RAB8B","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/RADX","total_profiled":1310},"omim":[{"mim_id":"301146","title":"RPA1-RELATED SINGLE-STRANDED DNA-BINDING PROTEIN, X-LINKED; RADX","url":"https://www.omim.org/entry/301146"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nuclear speckles","reliability":"Supported"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in many","driving_tissues":[{"tissue":"brain","ntpm":24.2},{"tissue":"pituitary gland","ntpm":19.2}],"url":"https://www.proteinatlas.org/search/RADX"},"hgnc":{"alias_symbol":["FLJ14191","FLJ10178"],"prev_symbol":["CXorf57"]},"alphafold":{"accession":"Q6NSI4","domains":[{"cath_id":"2.40.50.140","chopping":"44-188","consensus_level":"medium","plddt":86.5819,"start":44,"end":188},{"cath_id":"2.40.50.140","chopping":"217-350","consensus_level":"medium","plddt":88.567,"start":217,"end":350},{"cath_id":"2.40.50.140","chopping":"362-502","consensus_level":"high","plddt":87.9948,"start":362,"end":502},{"cath_id":"2.40.50.140","chopping":"524-565_676-705_744-852","consensus_level":"high","plddt":80.2961,"start":524,"end":852}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6NSI4","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q6NSI4-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q6NSI4-F1-predicted_aligned_error_v6.png","plddt_mean":75.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=RADX","jax_strain_url":"https://www.jax.org/strain/search?query=RADX"},"sequence":{"accession":"Q6NSI4","fasta_url":"https://rest.uniprot.org/uniprotkb/Q6NSI4.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q6NSI4/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q6NSI4"}},"corpus_meta":[{"pmid":"28735897","id":"PMC_28735897","title":"RADX Promotes Genome Stability and Modulates Chemosensitivity by Regulating RAD51 at Replication Forks.","date":"2017","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/28735897","citation_count":165,"is_preprint":false},{"pmid":"30021152","id":"PMC_30021152","title":"RADX Modulates RAD51 Activity to Control Replication Fork Protection.","date":"2018","source":"Cell reports","url":"https://pubmed.ncbi.nlm.nih.gov/30021152","citation_count":84,"is_preprint":false},{"pmid":"33453169","id":"PMC_33453169","title":"RADX controls RAD51 filament dynamics to regulate replication fork stability.","date":"2021","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/33453169","citation_count":32,"is_preprint":false},{"pmid":"29021206","id":"PMC_29021206","title":"RADX interacts with single-stranded DNA to promote replication fork stability.","date":"2017","source":"EMBO reports","url":"https://pubmed.ncbi.nlm.nih.gov/29021206","citation_count":29,"is_preprint":false},{"pmid":"34107305","id":"PMC_34107305","title":"RADX prevents genome instability by confining replication fork reversal to stalled forks.","date":"2021","source":"Molecular cell","url":"https://pubmed.ncbi.nlm.nih.gov/34107305","citation_count":29,"is_preprint":false},{"pmid":"32621611","id":"PMC_32621611","title":"RADX condenses single-stranded DNA to antagonize RAD51 loading.","date":"2020","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/32621611","citation_count":20,"is_preprint":false},{"pmid":"38466836","id":"PMC_38466836","title":"Structure of RADX and mechanism for regulation of RAD51 nucleofilaments.","date":"2024","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/38466836","citation_count":6,"is_preprint":false},{"pmid":"35120927","id":"PMC_35120927","title":"Oligomerization of DNA replication regulatory protein RADX is essential to maintain replication fork stability.","date":"2022","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/35120927","citation_count":5,"is_preprint":false},{"pmid":"37572935","id":"PMC_37572935","title":"CRISPR-dependent Base Editing Screens Identify Separation of Function Mutants of RADX with Altered RAD51 Regulatory Activity.","date":"2023","source":"Journal of molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/37572935","citation_count":3,"is_preprint":false},{"pmid":"37786681","id":"PMC_37786681","title":"Structure of RADX and mechanism for regulation of RAD51 nucleofilaments.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37786681","citation_count":1,"is_preprint":false},{"pmid":"36833228","id":"PMC_36833228","title":"RADX Gene Variant May Predispose to Familial Asperger Syndrome.","date":"2023","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/36833228","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.11.26.25341110","title":"Cross-Program Secondary Analyses and Public Health Innovation: The RADx Data Hub as a Resource for Integrated COVID-19 Research","date":"2025-11-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.11.26.25341110","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6768,"output_tokens":2435,"usd":0.028414,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9655,"output_tokens":3093,"usd":0.0628,"stage2_stop_reason":"end_turn"},"total_usd":0.091214,"stage1_batch_id":"msgbatch_01CNoDbkChHEkgrJnL7BwtGJ","stage2_batch_id":"msgbatch_016Y4x9E9Wg5VQDANj9quSQD","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2017,\n      \"finding\": \"RADX was identified as an RPA-like, single-strand DNA (ssDNA) binding protein that is recruited to replication forks, where it antagonizes RAD51 to prevent fork collapse. Inactivation of RADX causes excessive RAD51 activity, leading to slowed replication elongation and double-strand breaks.\",\n      \"method\": \"Proteomic identification at replication forks, genetic depletion (siRNA/CRISPR), DNA fiber assays, γH2AX foci\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — reciprocal functional assays, multiple orthogonal methods (iPOND mass spec, fiber assays, DSB detection), replicated across multiple subsequent studies\",\n      \"pmids\": [\"28735897\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"RADX binds ssDNA via an N-terminal OB fold cluster, which mediates its recruitment to sites of replication stress. Disruption of RADX expression or ssDNA binding leads to enhanced replication fork stalling and degradation. A balanced interplay between RADX and RPA ssDNA-binding activities is critical for replication integrity.\",\n      \"method\": \"Biochemical ssDNA binding assays, OB-fold deletion/mutation analysis, immunofluorescence at replication stress sites, DNA fiber assays\",\n      \"journal\": \"EMBO reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — in vitro ssDNA binding with domain mapping, cellular localization with functional consequence, two orthogonal methods in one study\",\n      \"pmids\": [\"29021206\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"RADX antagonizes RAD51 at stalled replication forks by competing with RAD51 for binding to ssDNA. Silencing RADX restores fork protection in cells deficient for BRCA1, BRCA2, FANCA, FANCD2, or BOD1L. RADX overexpression causes fork degradation dependent on MRE11 and DNA2 nucleases and requires fork reversal. The level of RAD51 determines fork fate, with more RAD51 required for protection than reversal.\",\n      \"method\": \"DNA fiber assays, siRNA knockdown in multiple BRCA/Fanconi pathway-deficient cell lines, RADX overexpression, nuclease inhibitor experiments\",\n      \"journal\": \"Cell reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple genetic backgrounds tested, multiple orthogonal methods, functional competition between RADX and RAD51 for ssDNA demonstrated biochemically\",\n      \"pmids\": [\"30021152\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"RADX condenses ssDNA filaments even when coated with RPA at physiological protein ratios, forming higher-order assemblies that can capture ssDNA in trans. RADX blocks RPA displacement by RAD51 and prevents RAD51 loading onto ssDNA, acting as an ssDNA condensation protein.\",\n      \"method\": \"Single-molecule imaging (total internal reflection fluorescence microscopy), in vitro reconstitution with purified proteins, single-molecule curtains\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — single-molecule in vitro reconstitution with purified proteins, direct visualization of RADX condensation and RAD51 loading inhibition, multiple imaging conditions\",\n      \"pmids\": [\"32621611\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RADX directly inhibits RAD51 strand exchange and D-loop formation. RADX selectively interacts with ATP-bound RAD51, stimulates RAD51 ATP hydrolysis, and destabilizes RAD51 nucleofilaments. Both ssDNA binding and direct RAD51 interaction are required for RADX to maintain replication fork elongation rates. BRCA2 can overcome RADX-dependent RAD51 inhibition, establishing RADX and BRCA2 as opposing regulators of RAD51 nucleofilament stability.\",\n      \"method\": \"In vitro strand exchange assay, D-loop assay, ATPase assay, biochemical interaction studies with ATP-bound RAD51, genetic complementation with BRCA2, DNA fiber assays\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — multiple in vitro biochemical assays (strand exchange, ATPase, D-loop), mutagenesis, epistasis with BRCA2, replicated across two orthogonal method classes\",\n      \"pmids\": [\"33453169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"RADX can either inhibit or promote fork reversal depending on replication stress levels: it inhibits fork reversal at elongating forks to prevent collapse, but at persistently stalled forks, RADX localizes to promote reversed fork structure formation. RADX increases SMARCAL1-dependent fork reversal when pre-bound RAD51 is inhibitory, acting via direct interaction with both RAD51 and ssDNA.\",\n      \"method\": \"DNA fiber assays, electron microscopy of replication intermediates, genetic epistasis with RTEL1 and fork protection factors, in vitro fork reversal assay with SMARCAL1 and RADX\",\n      \"journal\": \"Molecular cell\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Strong — EM visualization of fork structures, in vitro reconstitution with SMARCAL1, genetic epistasis with RTEL1 and fork protection factors, multiple orthogonal methods\",\n      \"pmids\": [\"34107305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"RADX functions as a homo-oligomer to regulate replication fork stability. RADX oligomerizes via at least two interaction surfaces, including a C-terminal region. Mutations preventing oligomerization abolish RADX function in cells, and this can be rescued by addition of a heterologous dimerization domain.\",\n      \"method\": \"Biochemical oligomerization assays, mutagenesis of oligomerization surfaces, complementation with heterologous dimerization domain, DNA fiber assays in cells\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — biochemical oligomerization mapping with mutagenesis, functional rescue experiments in cells, two orthogonal methods\",\n      \"pmids\": [\"35120927\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"CRISPR base editing screen identified RADX separation-of-function mutants that bind DNA and RAD51 but have reduced ability to stimulate RAD51 ATP hydrolysis. Cells expressing these mutants accumulate RAD51 on chromatin, exhibit replication defects, accumulate DNA damage, and are hypersensitive to replication stress, indicating that RADX must promote RAD51 ATP turnover to regulate genome stability during DNA replication.\",\n      \"method\": \"CRISPR base editing screen, ATPase assay, chromatin fractionation, DNA fiber assay, DNA damage sensitivity assays\",\n      \"journal\": \"Journal of molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 / Moderate — base editing screen with functional follow-up, in vitro ATPase validation of separation-of-function mutants, multiple cellular readouts\",\n      \"pmids\": [\"37572935\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"Cryo-EM structure of RADX (no structurally characterized orthologs) determined ab initio at 2–4 Å resolution. RADX forms concentration-dependent oligomeric states (predominantly trimers in the presence of ssDNA). The structure reveals the molecular basis for oligomerization and multivalent ssDNA binding. Negative stain EM imaging shows a RADX oligomer at the end of RAD51 filaments, supporting a model in which RADX caps and restricts RAD51 filament ends.\",\n      \"method\": \"Cryo-EM structure determination, mass photometry (oligomeric state analysis), negative stain EM of RADX-RAD51 filament complexes\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — high-resolution cryo-EM structure with functional validation by negative stain EM of RADX-RAD51 complexes, mass photometry, multiple orthogonal structural methods in one study\",\n      \"pmids\": [\"38466836\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"RADX is an RPA-like ssDNA-binding protein that forms homo-oligomers (predominantly trimers) via OB fold domains, binds ssDNA multivalently, and directly interacts with ATP-bound RAD51 at replication forks to stimulate its ATPase activity, destabilize RAD51 nucleofilaments, and block RAD51-mediated strand exchange — thereby counteracting BRCA2 to confine fork reversal to persistently stalled forks, prevent excessive fork slowing, and maintain genome stability.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"RADX is an RPA-like single-stranded DNA (ssDNA)-binding protein that operates at replication forks to restrain RAD51 activity and thereby preserve genome stability [#0]. It binds ssDNA through an N-terminal OB-fold cluster that mediates its recruitment to sites of replication stress, and its activity is balanced against that of RPA to maintain replication integrity [#1]. RADX antagonizes RAD51 by two cooperating mechanisms: it competes with RAD51 for ssDNA and condenses RPA-coated ssDNA into higher-order assemblies that block RPA displacement and prevent RAD51 loading [#2, #3], and it directly engages ATP-bound RAD51 to stimulate RAD51 ATP hydrolysis, destabilize RAD51 nucleofilaments, and inhibit strand exchange and D-loop formation — an activity that BRCA2 can override, establishing RADX and BRCA2 as opposing regulators of filament stability [#4, #7]. Through this regulation RADX confines fork reversal: it suppresses reversal at elongating forks to prevent collapse but promotes SMARCAL1-dependent reversal at persistently stalled forks when pre-bound RAD51 is inhibitory [#5]. RADX functions as a homo-oligomer — predominantly a trimer on ssDNA — assembled via multiple interaction surfaces including a C-terminal region, and structural analysis indicates it caps and restricts RAD51 filament ends [#6, #8].\"\n,\n  \"teleology\": [\n    {\n      \"year\": 2017,\n      \"claim\": \"Established RADX as a previously uncharacterized fork-associated ssDNA-binding factor whose loss destabilizes replication, framing it as a RAD51 antagonist rather than a generic fork protein.\",\n      \"evidence\": \"Proteomic identification at forks with siRNA/CRISPR depletion, DNA fiber assays, and γH2AX foci\",\n      \"pmids\": [\"28735897\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not resolve whether antagonism is via ssDNA competition or direct RAD51 binding\", \"No structural or biochemical mechanism for fork recruitment\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Mapped the ssDNA-binding determinant to an N-terminal OB-fold cluster and tied that binding to stress-site recruitment, defining the biochemical basis of RADX localization.\",\n      \"evidence\": \"In vitro ssDNA binding with OB-fold deletion/mutation, immunofluorescence, and DNA fiber assays\",\n      \"pmids\": [\"29021206\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not establish how RADX-RPA balance is set quantitatively\", \"Did not test direct RAD51 contact\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Showed RADX competes with RAD51 for ssDNA and that RAD51 dosage dictates fork fate, explaining why RADX loss rescues fork protection in BRCA/Fanconi-deficient cells.\",\n      \"evidence\": \"DNA fiber assays across multiple BRCA/Fanconi-deficient lines, overexpression, and nuclease-inhibitor experiments\",\n      \"pmids\": [\"30021152\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Competition demonstrated functionally but not at single-molecule resolution\", \"Direct RADX-RAD51 protein interaction not yet shown\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Resolved the ssDNA-level mechanism by showing RADX condenses even RPA-coated ssDNA and blocks RPA displacement, recasting RADX as an ssDNA condensation protein that prevents RAD51 loading.\",\n      \"evidence\": \"Single-molecule TIRF imaging and ssDNA curtains with purified proteins\",\n      \"pmids\": [\"32621611\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Did not address whether RADX also acts on assembled RAD51 filaments\", \"In vitro ratios may not capture in vivo regulation\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Identified a second, direct mechanism: RADX binds ATP-bound RAD51, stimulates its ATPase, destabilizes nucleofilaments and blocks strand exchange, and placed RADX opposite BRCA2 in RAD51 filament regulation.\",\n      \"evidence\": \"In vitro strand exchange, D-loop and ATPase assays, ATP-state-selective interaction studies, and BRCA2 epistasis with fiber assays\",\n      \"pmids\": [\"33453169\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of the ATP-bound-RAD51 interaction not defined\", \"Quantitative interplay with the ssDNA-condensation activity unresolved\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Reconciled RADX's apparently opposing roles by showing it inhibits reversal at elongating forks but promotes SMARCAL1-dependent reversal at persistently stalled forks, making fork outcome stress-dependent.\",\n      \"evidence\": \"DNA fiber assays, electron microscopy of replication intermediates, RTEL1 epistasis, and in vitro SMARCAL1 fork reversal reconstitution\",\n      \"pmids\": [\"34107305\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Signal that switches RADX between inhibitory and promoting modes is unknown\", \"Threshold defining 'persistent' stalling not defined\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Demonstrated that homo-oligomerization, via multiple surfaces including a C-terminal region, is obligatory for RADX function in cells.\",\n      \"evidence\": \"Oligomerization mapping with mutagenesis, heterologous dimerization-domain rescue, and DNA fiber assays\",\n      \"pmids\": [\"35120927\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Oligomeric stoichiometry on ssDNA not yet defined\", \"Did not resolve oligomer architecture structurally\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Used separation-of-function mutants to prove that RADX must actively promote RAD51 ATP turnover — not merely bind DNA and RAD51 — to maintain genome stability.\",\n      \"evidence\": \"CRISPR base-editing screen with ATPase, chromatin fractionation, fiber, and damage-sensitivity assays\",\n      \"pmids\": [\"37572935\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic mechanism by which RADX stimulates RAD51 ATPase not defined\", \"Did not separate ssDNA-condensation from ATPase-stimulation contributions in vivo\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Provided the first RADX structure, defining oligomerization and multivalent ssDNA binding and visualizing RADX capping RAD51 filament ends, giving a physical model for filament restriction.\",\n      \"evidence\": \"Ab initio cryo-EM at 2–4 Å, mass photometry, and negative-stain EM of RADX-RAD51 filament complexes\",\n      \"pmids\": [\"38466836\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No high-resolution structure of the RADX-RAD51 interface\", \"Capping model not yet tested with structure-guided interface mutants in cells\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the two RADX activities (ssDNA condensation versus direct RAD51 ATPase stimulation/filament capping) are coordinated and toggled by replication-stress signals to choose fork elongation versus reversal remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"High\",\n      \"gaps\": [\"No mechanism for sensing 'persistent' stalling\", \"No structure of the RADX-RAD51 complex interface\", \"Upstream regulation/post-translational control of RADX unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [2, 4, 5, 7]},\n      {\"term_id\": \"GO:0140313\", \"supporting_discovery_ids\": [2, 3]}\n    ],\n    \"localization\": [],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [0, 1, 2, 5]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 4, 5]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"RAD51\", \"RPA\", \"BRCA2\", \"SMARCAL1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}