{"gene":"HROB","run_date":"2026-04-28T18:06:53","timeline":{"discoveries":[{"year":2019,"finding":"HROB (C17orf53) is an OB-fold-containing factor that recruits the MCM8-MCM9 helicase to sites of DNA damage to promote recombination-associated DNA synthesis downstream of RAD51, acting analogously to bacteriophage T4 gp59 helicase loader.","method":"Genetic epistasis, loss-of-function (knockout mouse and cell lines), recruitment assays at DNA damage sites, phenotypic readouts (HR defects, meiotic arrest, infertility)","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — reciprocal functional assays, epistasis with HELQ, in vivo mouse model, replicated by multiple labs","pmids":["31467087"],"is_preprint":false},{"year":2019,"finding":"The HROB-MCM8-MCM9 pathway acts redundantly with the HELQ helicase; cells lacking both HROB and HELQ have severely impaired HR, placing them in two parallel routes for HR completion downstream of RAD51.","method":"Genetic epistasis (double-mutant HROB/HELQ cells), HR assays","journal":"Genes & development","confidence":"High","confidence_rationale":"Tier 2 — double-mutant epistasis with defined HR phenotype in multiple cell lines","pmids":["31467087"],"is_preprint":false},{"year":2020,"finding":"HROB (MCM8IP/C17orf53) directly binds single-stranded DNA and RPA1, directly associates with the MCM8-9 helicase complex, and stimulates the helicase activity of MCM8-9 in vitro; these interactions are required for HR-dependent DNA synthesis (long-tract gene conversion) and replication fork progression after crosslinking damage.","method":"Co-immunoprecipitation, in vitro helicase activity assay, ssDNA binding assay, loss-of-function (MCM8IP-deficient cells) with HR and fork progression readouts","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1-2 — in vitro reconstitution of helicase stimulation combined with reciprocal Co-IP and cellular phenotypes, independent lab from paper 1","pmids":["32528060"],"is_preprint":false},{"year":2020,"finding":"HROB (C17orf53) is a ssDNA- and RPA-binding protein; both activities are important for its function in interstrand crosslink (ICL) repair, and it works together with MCM8/9 to promote cell survival after ICL damage.","method":"Biochemical binding assays (ssDNA, RPA), genome-wide ATR-inhibitor fitness screen, multi-omics interaction mapping, ICL sensitivity assays in loss-of-function cells","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 2 — multiple orthogonal methods, independent replication of MCM8/9 interaction","pmids":["32853826"],"is_preprint":false},{"year":2024,"finding":"HROB makes transient contacts with both MCM8 and MCM9 subunits and binds the MCM8-9 heterodimer with highest affinity. MCM8-9 unwinds DNA as a hexamer assembled from dimers on DNA in the presence of ATP, with two alternating interfaces—one stable (obligate heterodimer, where HROB binds) and one labile (mediating hexamer assembly). HROB does not affect hexamer ring formation on ssDNA but promotes DNA unwinding downstream, likely by coordinating ATP hydrolysis with structural transitions during translocation; the ATPase site at the labile interface contributes disproportionately more to unwinding than that at the stable interface.","method":"Molecular modeling/biochemistry (interaction interface mapping), in vitro helicase assay, single-molecule experiments, ATPase assays, mutagenesis of interface residues","journal":"Nature communications","confidence":"High","confidence_rationale":"Tier 1 — reconstitution, biochemistry, single-molecule imaging, mutagenesis, structure-function analysis in one study","pmids":["38678026"],"is_preprint":false},{"year":2024,"finding":"HROB is a nuclear protein expressed in a cell-cycle-dependent manner with peak levels in S phase and downregulation in quiescence; FRET-based assays detected associations between HROB and proteins of the DNA replication machinery; ectopic overexpression of HROB nearly completely shuts down DNA replication.","method":"Flow cytometry FRET assay, cell-cycle fractionation/expression analysis, ectopic overexpression with DNA replication readout","journal":"Genes","confidence":"Medium","confidence_rationale":"Tier 3 — FRET-based interaction and overexpression phenotype, single lab, no mechanistic dissection of replication complex","pmids":["39766854"],"is_preprint":false},{"year":2025,"finding":"HROB interacts with ZC3HC1 and reduces its phosphorylation at Ser354; this de-phosphorylation facilitates K27-linked ubiquitination of CCNB1, promoting its proteasomal degradation and impairing G2-to-M phase transition, thereby suppressing cell proliferation.","method":"Co-immunoprecipitation, phosphorylation assays, ubiquitination assays, loss-of-function/overexpression with cell cycle and proliferation readouts","journal":"Cancer science","confidence":"Medium","confidence_rationale":"Tier 2-3 — multiple biochemical assays in one lab, mechanistic pathway defined but not yet independently replicated","pmids":["40654113"],"is_preprint":false},{"year":2025,"finding":"HROB is required for MCM9 recruitment to ICL-induced nuclear foci; the BRCv motif and HROB are needed for MCM8/9 foci formation but not for FANCD2 binding, indicating HROB functions in the functional activation step of MCM8/9 rather than in physical association with FANCD2.","method":"Immunofluorescence, co-immunoprecipitation, knockout cell lines (MCM8, MCM9), epistasis analysis (γH2AX and survival assays in combined knockouts)","journal":"bioRxiv","confidence":"Medium","confidence_rationale":"Tier 2 — Co-IP + IF + epistasis, preprint not yet peer-reviewed","pmids":["bio_10.1101_2025.08.07.669127"],"is_preprint":true}],"current_model":"HROB is an OB-fold-containing, ssDNA- and RPA-binding nuclear protein that acts as a loader/activator of the MCM8-MCM9 helicase complex: it directly contacts both MCM8 and MCM9 subunits, stimulates MCM8-9 ATPase and helicase activities, and recruits the hexameric MCM8-9 ring to DNA damage sites (particularly branched HR intermediates and interstrand crosslinks) to drive recombination-associated DNA synthesis downstream of RAD51, functioning in a pathway parallel to the HELQ helicase and downstream of the Fanconi anemia factor FANCD2."},"narrative":{"teleology":[{"year":2019,"claim":"Identification of HROB as the MCM8-9 helicase loader resolved how this replicative helicase is recruited to DNA damage sites for recombination-associated DNA synthesis, establishing a T4 gp59-like loading paradigm in vertebrate HR.","evidence":"Knockout mouse and cell lines with HR assays, recruitment imaging at damage sites, genetic epistasis with HELQ","pmids":["31467087"],"confidence":"High","gaps":["Mechanism by which HROB stimulates MCM8-9 activity was unknown","Whether HROB binds DNA or RPA directly was not addressed","Structural basis of the HROB–MCM8-9 interaction was undefined"]},{"year":2020,"claim":"Biochemical reconstitution showed HROB directly binds ssDNA and RPA1 and stimulates MCM8-9 helicase activity in vitro, establishing it as a bona fide activator — not merely a recruitment scaffold — and linking these activities to long-tract gene conversion and replication fork progression through interstrand crosslinks.","evidence":"In vitro helicase and ssDNA-binding assays, reciprocal Co-IP, ICL sensitivity in MCM8IP-deficient cells (two independent labs)","pmids":["32528060","32853826"],"confidence":"High","gaps":["Whether HROB influences MCM8-9 hexamer assembly or acts post-assembly was unknown","Which subunit interface HROB contacts was not mapped","Relationship to the Fanconi anemia pathway (e.g., FANCD2) was not mechanistically resolved"]},{"year":2024,"claim":"Structure-function analysis revealed that MCM8-9 assembles as a hexamer from dimers with two alternating interfaces, and HROB binds specifically at the stable (obligate) heterodimer interface to promote DNA unwinding — likely by coordinating ATP hydrolysis with translocation — without affecting hexamer ring formation on ssDNA.","evidence":"Single-molecule imaging, in vitro ATPase assays, interface mutagenesis, molecular modeling","pmids":["38678026"],"confidence":"High","gaps":["Atomic-resolution structure of the HROB–MCM8-9 complex is lacking","How HROB coordinates ATPase firing at the labile versus stable interface remains mechanistically unclear","In vivo validation of the proposed hexameric translocation model is absent"]},{"year":2024,"claim":"Cell-cycle profiling established that HROB expression peaks in S phase and is downregulated in quiescence, and FRET-based assays detected proximity to replication machinery components, suggesting a regulated connection between HROB and DNA replication beyond its known repair role.","evidence":"Flow cytometry FRET, cell-cycle fractionation, ectopic overexpression with replication readouts","pmids":["39766854"],"confidence":"Medium","gaps":["Identity of the replication machinery components detected by FRET was not resolved to specific factors","The mechanism by which HROB overexpression inhibits replication is undefined","Whether the S-phase expression pattern reflects a replication function distinct from repair is untested"]},{"year":2025,"claim":"A reported interaction with ZC3HC1 linked HROB to cell-cycle regulation through CCNB1 ubiquitination and degradation, suggesting a non-canonical role in controlling the G2/M transition independent of its MCM8-9 loading function.","evidence":"Co-immunoprecipitation, phosphorylation and ubiquitination assays, overexpression/loss-of-function with proliferation readouts","pmids":["40654113"],"confidence":"Medium","gaps":["Not yet independently replicated by a second laboratory","Whether this ZC3HC1 pathway operates in physiological contexts or only upon overexpression is unclear","Relationship between the MCM8-9 loading function and CCNB1 regulation has not been tested"]},{"year":null,"claim":"Key open questions include the atomic structure of the HROB–MCM8-9 complex, the mechanism by which HROB coordinates ATPase-driven translocation, whether HROB has a direct role in unperturbed DNA replication, and whether its reported cell-cycle regulatory function via ZC3HC1/CCNB1 is physiologically relevant.","evidence":"","pmids":[],"confidence":"Low","gaps":["No high-resolution structure of the HROB–MCM8-9 complex exists","Physiological relevance of the ZC3HC1–CCNB1 axis awaits independent confirmation","Whether HROB functions at replication forks in the absence of damage is untested"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[2,3]},{"term_id":"GO:0098772","term_label":"molecular function regulator activity","supporting_discovery_ids":[0,2,4]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,5,7]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,1,2,3,4,7]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,6]}],"complexes":["MCM8-MCM9-HROB"],"partners":["MCM8","MCM9","RPA1","ZC3HC1"],"other_free_text":[]},"mechanistic_narrative":"HROB (C17orf53) is an OB-fold-containing nuclear protein that functions as a dedicated loader and activator of the MCM8-MCM9 helicase complex during homologous recombination and interstrand crosslink repair. It binds single-stranded DNA and RPA1, directly contacts both MCM8 and MCM9 subunits at the stable heterodimer interface, and stimulates MCM8-9 ATPase and helicase activities to drive recombination-associated DNA synthesis downstream of RAD51, acting in a pathway parallel to the HELQ helicase [PMID:31467087, PMID:32528060, PMID:38678026]. HROB is expressed in a cell-cycle-dependent manner with peak levels in S phase, and its ssDNA- and RPA-binding activities are required for cell survival after crosslinking damage [PMID:32853826, PMID:39766854]. Loss of HROB in mice causes meiotic arrest and infertility, phenocopying MCM8/MCM9 deficiency [PMID:31467087]."},"prefetch_data":{"uniprot":{"accession":"Q8N3J3","full_name":"Homologous recombination OB-fold protein","aliases":[],"length_aa":647,"mass_kda":69.8,"function":"DNA-binding protein involved in homologous recombination that acts by recruiting the MCM8-MCM9 helicase complex to sites of DNA damage to promote DNA repair synthesis (PubMed:31467087). A C-terminal region including the OB-fold stimulates the helicase activity of MCM8-MCM9 probably by altering its conformation (PubMed:37535404)","subcellular_location":"Nucleus; Chromosome","url":"https://www.uniprot.org/uniprotkb/Q8N3J3/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/HROB","classification":"Not Classified","n_dependent_lines":59,"n_total_lines":1208,"dependency_fraction":0.048841059602649006},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"MSH6","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/HROB","total_profiled":1310},"omim":[{"mim_id":"620897","title":"OVARIAN DYSGENESIS 11; ODG11","url":"https://www.omim.org/entry/620897"},{"mim_id":"618611","title":"HOMOLOGOUS RECOMBINATION FACTOR WITH OB-FOLD; HROB","url":"https://www.omim.org/entry/618611"},{"mim_id":"618078","title":"OVARIAN DYSGENESIS 6; ODG6","url":"https://www.omim.org/entry/618078"},{"mim_id":"608193","title":"REC8 MEIOTIC RECOMBINATION PROTEIN; REC8","url":"https://www.omim.org/entry/608193"},{"mim_id":"607617","title":"NUCLEOPORIN, 107-KD; NUP107","url":"https://www.omim.org/entry/607617"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Approved","locations":[{"location":"Nucleoplasm","reliability":"Approved"},{"location":"Cytosol","reliability":"Approved"}],"tissue_specificity":"Tissue enhanced","tissue_distribution":"Detected in some","driving_tissues":[{"tissue":"bone marrow","ntpm":8.8},{"tissue":"testis","ntpm":10.7}],"url":"https://www.proteinatlas.org/search/HROB"},"hgnc":{"alias_symbol":["MGC3130","MCM8IP"],"prev_symbol":["C17orf53"]},"alphafold":{"accession":"Q8N3J3","domains":[{"cath_id":"2.40.50.140","chopping":"453-574","consensus_level":"high","plddt":91.0668,"start":453,"end":574}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N3J3","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N3J3-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q8N3J3-F1-predicted_aligned_error_v6.png","plddt_mean":54.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=HROB","jax_strain_url":"https://www.jax.org/strain/search?query=HROB"},"sequence":{"accession":"Q8N3J3","fasta_url":"https://rest.uniprot.org/uniprotkb/Q8N3J3.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q8N3J3/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q8N3J3"}},"corpus_meta":[{"pmid":"31467087","id":"PMC_31467087","title":"Control of homologous recombination by the HROB-MCM8-MCM9 pathway.","date":"2019","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/31467087","citation_count":62,"is_preprint":false},{"pmid":"32528060","id":"PMC_32528060","title":"MCM8IP activates the MCM8-9 helicase to promote DNA synthesis and homologous recombination upon DNA damage.","date":"2020","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/32528060","citation_count":44,"is_preprint":false},{"pmid":"34707299","id":"PMC_34707299","title":"Meiotic genes in premature ovarian insufficiency: variants in HROB and REC8 as likely genetic causes.","date":"2021","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/34707299","citation_count":36,"is_preprint":false},{"pmid":"32853826","id":"PMC_32853826","title":"C17orf53 is identified as a novel gene involved in inter-strand crosslink repair.","date":"2020","source":"DNA repair","url":"https://pubmed.ncbi.nlm.nih.gov/32853826","citation_count":24,"is_preprint":false},{"pmid":"31575675","id":"PMC_31575675","title":"Ways to unwind with HROB, a new player in homologous recombination.","date":"2019","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/31575675","citation_count":11,"is_preprint":false},{"pmid":"38678026","id":"PMC_38678026","title":"Mechanism of DNA unwinding by MCM8-9 in complex with HROB.","date":"2024","source":"Nature communications","url":"https://pubmed.ncbi.nlm.nih.gov/38678026","citation_count":10,"is_preprint":false},{"pmid":"35903352","id":"PMC_35903352","title":"Pan-Cancer Analysis Identified Homologous Recombination Factor With OB-Fold (HROB) as a Potential Biomarker for Various Tumor Types.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35903352","citation_count":4,"is_preprint":false},{"pmid":"39766854","id":"PMC_39766854","title":"HROB Is Implicated in DNA Replication.","date":"2024","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/39766854","citation_count":1,"is_preprint":false},{"pmid":"37461676","id":"PMC_37461676","title":"Mechanism of DNA unwinding by hexameric MCM8-9 in complex with HROB.","date":"2023","source":"Research square","url":"https://pubmed.ncbi.nlm.nih.gov/37461676","citation_count":1,"is_preprint":false},{"pmid":"38105698","id":"PMC_38105698","title":"Genetic analysis of novel pathogenic gene HROB in a family with primary ovarian insufficiency.","date":"2023","source":"Zhejiang da xue xue bao. Yi xue ban = Journal of Zhejiang University. Medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/38105698","citation_count":1,"is_preprint":false},{"pmid":"40654113","id":"PMC_40654113","title":"HROB Induces Lung Adenocarcinoma Progression via ZC3HC1-CCNB1 Axis Regulation and Cell Cycle Dysregulation.","date":"2025","source":"Cancer science","url":"https://pubmed.ncbi.nlm.nih.gov/40654113","citation_count":0,"is_preprint":false},{"pmid":"37398313","id":"PMC_37398313","title":"Mechanism of DNA unwinding by hexameric MCM8-9 in complex with HROB.","date":"2023","source":"bioRxiv : the preprint server for biology","url":"https://pubmed.ncbi.nlm.nih.gov/37398313","citation_count":0,"is_preprint":false},{"pmid":"41878782","id":"PMC_41878782","title":"Biallelic Germline Inactivation of HROB Causes Primary Gonadal Insufficiency and is Potentially Associated with Colonic Polyposis Predisposition.","date":"2026","source":"American journal of medical genetics. Part A","url":"https://pubmed.ncbi.nlm.nih.gov/41878782","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.08.07.669127","title":"MCM8/9 and FANCD2 interact within a shared pathway in response to replication stress caused by DNA crosslinks","date":"2025-08-07","source":"bioRxiv","url":"https://doi.org/10.1101/2025.08.07.669127","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":7293,"output_tokens":2009,"usd":0.026007},"stage2":{"model":"claude-opus-4-6","input_tokens":5286,"output_tokens":1859,"usd":0.109357},"total_usd":0.135364,"stage1_batch_id":"msgbatch_01DzrsgVgYngY1hvM3DU1yF2","stage2_batch_id":"msgbatch_01KA9b7iRzKFdhoBUT7vCvSe","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2019,\n      \"finding\": \"HROB (C17orf53) is an OB-fold-containing factor that recruits the MCM8-MCM9 helicase to sites of DNA damage to promote recombination-associated DNA synthesis downstream of RAD51, acting analogously to bacteriophage T4 gp59 helicase loader.\",\n      \"method\": \"Genetic epistasis, loss-of-function (knockout mouse and cell lines), recruitment assays at DNA damage sites, phenotypic readouts (HR defects, meiotic arrest, infertility)\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — reciprocal functional assays, epistasis with HELQ, in vivo mouse model, replicated by multiple labs\",\n      \"pmids\": [\"31467087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The HROB-MCM8-MCM9 pathway acts redundantly with the HELQ helicase; cells lacking both HROB and HELQ have severely impaired HR, placing them in two parallel routes for HR completion downstream of RAD51.\",\n      \"method\": \"Genetic epistasis (double-mutant HROB/HELQ cells), HR assays\",\n      \"journal\": \"Genes & development\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — double-mutant epistasis with defined HR phenotype in multiple cell lines\",\n      \"pmids\": [\"31467087\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HROB (MCM8IP/C17orf53) directly binds single-stranded DNA and RPA1, directly associates with the MCM8-9 helicase complex, and stimulates the helicase activity of MCM8-9 in vitro; these interactions are required for HR-dependent DNA synthesis (long-tract gene conversion) and replication fork progression after crosslinking damage.\",\n      \"method\": \"Co-immunoprecipitation, in vitro helicase activity assay, ssDNA binding assay, loss-of-function (MCM8IP-deficient cells) with HR and fork progression readouts\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1-2 — in vitro reconstitution of helicase stimulation combined with reciprocal Co-IP and cellular phenotypes, independent lab from paper 1\",\n      \"pmids\": [\"32528060\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2020,\n      \"finding\": \"HROB (C17orf53) is a ssDNA- and RPA-binding protein; both activities are important for its function in interstrand crosslink (ICL) repair, and it works together with MCM8/9 to promote cell survival after ICL damage.\",\n      \"method\": \"Biochemical binding assays (ssDNA, RPA), genome-wide ATR-inhibitor fitness screen, multi-omics interaction mapping, ICL sensitivity assays in loss-of-function cells\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — multiple orthogonal methods, independent replication of MCM8/9 interaction\",\n      \"pmids\": [\"32853826\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HROB makes transient contacts with both MCM8 and MCM9 subunits and binds the MCM8-9 heterodimer with highest affinity. MCM8-9 unwinds DNA as a hexamer assembled from dimers on DNA in the presence of ATP, with two alternating interfaces—one stable (obligate heterodimer, where HROB binds) and one labile (mediating hexamer assembly). HROB does not affect hexamer ring formation on ssDNA but promotes DNA unwinding downstream, likely by coordinating ATP hydrolysis with structural transitions during translocation; the ATPase site at the labile interface contributes disproportionately more to unwinding than that at the stable interface.\",\n      \"method\": \"Molecular modeling/biochemistry (interaction interface mapping), in vitro helicase assay, single-molecule experiments, ATPase assays, mutagenesis of interface residues\",\n      \"journal\": \"Nature communications\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — reconstitution, biochemistry, single-molecule imaging, mutagenesis, structure-function analysis in one study\",\n      \"pmids\": [\"38678026\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"HROB is a nuclear protein expressed in a cell-cycle-dependent manner with peak levels in S phase and downregulation in quiescence; FRET-based assays detected associations between HROB and proteins of the DNA replication machinery; ectopic overexpression of HROB nearly completely shuts down DNA replication.\",\n      \"method\": \"Flow cytometry FRET assay, cell-cycle fractionation/expression analysis, ectopic overexpression with DNA replication readout\",\n      \"journal\": \"Genes\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 — FRET-based interaction and overexpression phenotype, single lab, no mechanistic dissection of replication complex\",\n      \"pmids\": [\"39766854\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HROB interacts with ZC3HC1 and reduces its phosphorylation at Ser354; this de-phosphorylation facilitates K27-linked ubiquitination of CCNB1, promoting its proteasomal degradation and impairing G2-to-M phase transition, thereby suppressing cell proliferation.\",\n      \"method\": \"Co-immunoprecipitation, phosphorylation assays, ubiquitination assays, loss-of-function/overexpression with cell cycle and proliferation readouts\",\n      \"journal\": \"Cancer science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2-3 — multiple biochemical assays in one lab, mechanistic pathway defined but not yet independently replicated\",\n      \"pmids\": [\"40654113\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"HROB is required for MCM9 recruitment to ICL-induced nuclear foci; the BRCv motif and HROB are needed for MCM8/9 foci formation but not for FANCD2 binding, indicating HROB functions in the functional activation step of MCM8/9 rather than in physical association with FANCD2.\",\n      \"method\": \"Immunofluorescence, co-immunoprecipitation, knockout cell lines (MCM8, MCM9), epistasis analysis (γH2AX and survival assays in combined knockouts)\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — Co-IP + IF + epistasis, preprint not yet peer-reviewed\",\n      \"pmids\": [\"bio_10.1101_2025.08.07.669127\"],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"HROB is an OB-fold-containing, ssDNA- and RPA-binding nuclear protein that acts as a loader/activator of the MCM8-MCM9 helicase complex: it directly contacts both MCM8 and MCM9 subunits, stimulates MCM8-9 ATPase and helicase activities, and recruits the hexameric MCM8-9 ring to DNA damage sites (particularly branched HR intermediates and interstrand crosslinks) to drive recombination-associated DNA synthesis downstream of RAD51, functioning in a pathway parallel to the HELQ helicase and downstream of the Fanconi anemia factor FANCD2.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"HROB (C17orf53) is an OB-fold-containing nuclear protein that functions as a dedicated loader and activator of the MCM8-MCM9 helicase complex during homologous recombination and interstrand crosslink repair. It binds single-stranded DNA and RPA1, directly contacts both MCM8 and MCM9 subunits at the stable heterodimer interface, and stimulates MCM8-9 ATPase and helicase activities to drive recombination-associated DNA synthesis downstream of RAD51, acting in a pathway parallel to the HELQ helicase [PMID:31467087, PMID:32528060, PMID:38678026]. HROB is expressed in a cell-cycle-dependent manner with peak levels in S phase, and its ssDNA- and RPA-binding activities are required for cell survival after crosslinking damage [PMID:32853826, PMID:39766854]. Loss of HROB in mice causes meiotic arrest and infertility, phenocopying MCM8/MCM9 deficiency [PMID:31467087].\",\n  \"teleology\": [\n    {\n      \"year\": 2019,\n      \"claim\": \"Identification of HROB as the MCM8-9 helicase loader resolved how this replicative helicase is recruited to DNA damage sites for recombination-associated DNA synthesis, establishing a T4 gp59-like loading paradigm in vertebrate HR.\",\n      \"evidence\": \"Knockout mouse and cell lines with HR assays, recruitment imaging at damage sites, genetic epistasis with HELQ\",\n      \"pmids\": [\"31467087\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Mechanism by which HROB stimulates MCM8-9 activity was unknown\",\n        \"Whether HROB binds DNA or RPA directly was not addressed\",\n        \"Structural basis of the HROB–MCM8-9 interaction was undefined\"\n      ]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Biochemical reconstitution showed HROB directly binds ssDNA and RPA1 and stimulates MCM8-9 helicase activity in vitro, establishing it as a bona fide activator — not merely a recruitment scaffold — and linking these activities to long-tract gene conversion and replication fork progression through interstrand crosslinks.\",\n      \"evidence\": \"In vitro helicase and ssDNA-binding assays, reciprocal Co-IP, ICL sensitivity in MCM8IP-deficient cells (two independent labs)\",\n      \"pmids\": [\"32528060\", \"32853826\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Whether HROB influences MCM8-9 hexamer assembly or acts post-assembly was unknown\",\n        \"Which subunit interface HROB contacts was not mapped\",\n        \"Relationship to the Fanconi anemia pathway (e.g., FANCD2) was not mechanistically resolved\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Structure-function analysis revealed that MCM8-9 assembles as a hexamer from dimers with two alternating interfaces, and HROB binds specifically at the stable (obligate) heterodimer interface to promote DNA unwinding — likely by coordinating ATP hydrolysis with translocation — without affecting hexamer ring formation on ssDNA.\",\n      \"evidence\": \"Single-molecule imaging, in vitro ATPase assays, interface mutagenesis, molecular modeling\",\n      \"pmids\": [\"38678026\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Atomic-resolution structure of the HROB–MCM8-9 complex is lacking\",\n        \"How HROB coordinates ATPase firing at the labile versus stable interface remains mechanistically unclear\",\n        \"In vivo validation of the proposed hexameric translocation model is absent\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Cell-cycle profiling established that HROB expression peaks in S phase and is downregulated in quiescence, and FRET-based assays detected proximity to replication machinery components, suggesting a regulated connection between HROB and DNA replication beyond its known repair role.\",\n      \"evidence\": \"Flow cytometry FRET, cell-cycle fractionation, ectopic overexpression with replication readouts\",\n      \"pmids\": [\"39766854\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Identity of the replication machinery components detected by FRET was not resolved to specific factors\",\n        \"The mechanism by which HROB overexpression inhibits replication is undefined\",\n        \"Whether the S-phase expression pattern reflects a replication function distinct from repair is untested\"\n      ]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"A reported interaction with ZC3HC1 linked HROB to cell-cycle regulation through CCNB1 ubiquitination and degradation, suggesting a non-canonical role in controlling the G2/M transition independent of its MCM8-9 loading function.\",\n      \"evidence\": \"Co-immunoprecipitation, phosphorylation and ubiquitination assays, overexpression/loss-of-function with proliferation readouts\",\n      \"pmids\": [\"40654113\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Not yet independently replicated by a second laboratory\",\n        \"Whether this ZC3HC1 pathway operates in physiological contexts or only upon overexpression is unclear\",\n        \"Relationship between the MCM8-9 loading function and CCNB1 regulation has not been tested\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key open questions include the atomic structure of the HROB–MCM8-9 complex, the mechanism by which HROB coordinates ATPase-driven translocation, whether HROB has a direct role in unperturbed DNA replication, and whether its reported cell-cycle regulatory function via ZC3HC1/CCNB1 is physiologically relevant.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\n        \"No high-resolution structure of the HROB–MCM8-9 complex exists\",\n        \"Physiological relevance of the ZC3HC1–CCNB1 axis awaits independent confirmation\",\n        \"Whether HROB functions at replication forks in the absence of damage is untested\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [2, 3]},\n      {\"term_id\": \"GO:0098772\", \"supporting_discovery_ids\": [0, 2, 4]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 5, 7]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 1, 2, 3, 4, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 6]}\n    ],\n    \"complexes\": [\n      \"MCM8-MCM9-HROB\"\n    ],\n    \"partners\": [\n      \"MCM8\",\n      \"MCM9\",\n      \"RPA1\",\n      \"ZC3HC1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}