{"gene":"NABP1","run_date":"2026-04-29T11:37:56","timeline":{"discoveries":[{"year":2006,"finding":"NABP1 (nucleic acid binding protein 1) contains an OB (oligonucleotide/oligosaccharide binding) motif at its N-terminus, localizes to the nucleus as shown by confocal microscopy, is part of a high molecular-mass nuclear protein complex as determined by size-exclusion chromatography, and binds single-stranded nucleic acids but not double-stranded DNA in direct binding assays.","method":"Confocal microscopy, size-exclusion chromatography, nucleic acid binding assays","journal":"The Biochemical journal","confidence":"Medium","confidence_rationale":"Tier 2 — direct localization and binding experiments with functional consequence, single lab","pmids":["16533169"],"is_preprint":false},{"year":2015,"finding":"The C-terminal tail of NABP1 (hSSB2) is essential for its DNA binding functionality; deletion of the C-terminal tail reduces ssDNA binding affinity, and the C-terminal tail is responsible for NABP1 multimerization on ssDNA. Both NABP1 and NABP2 exist as monomers in solution and prefer ssDNA over dsDNA, but NABP1 has higher affinity for ssDNA than NABP2, whereas NABP2 has higher affinity for ssRNA than NABP1.","method":"EMSA, ITC, sucrose gradient centrifugation, circular dichroism spectroscopy","journal":"Biochimica et biophysica acta","confidence":"High","confidence_rationale":"Tier 1 — multiple orthogonal in vitro biochemical assays with deletion mutagenesis in a single study","pmids":["26550690"],"is_preprint":false},{"year":2017,"finding":"NMR backbone resonance assignments of the OB domain of hSSB2 (NABP1) mapped the ssDNA interaction interface, revealing that ssDNA binding is driven by four key aromatic residues, analogous to hSSB1, though with significant differences in chemical shift perturbations reflecting differences in ssDNA recognition.","method":"NMR solution-state spectroscopy, chemical shift perturbation mapping","journal":"Biomolecular NMR assignments","confidence":"Medium","confidence_rationale":"Tier 1 — NMR structural mapping, single lab","pmids":["29063999"],"is_preprint":false},{"year":2019,"finding":"The OB domain of hSSB2 (NABP1) recognizes cyclobutane pyrimidine dimers (CPDs) in ssDNA; four key aromatic residues (W59, Y78, W82, Y89) are responsible for ssDNA/CPD recognition as determined by NMR chemical shift mapping and biolayer interferometry. hSSB2 also binds duplex DNA with a two-base mismatch mimicking a CPD.","method":"Biolayer interferometry, NMR chemical shift mapping, mutagenesis","journal":"Proteins","confidence":"High","confidence_rationale":"Tier 1 — structural NMR plus biophysical binding assays with identified residues, single lab with multiple orthogonal methods","pmids":["31443132"],"is_preprint":false},{"year":2021,"finding":"hSSB2 (NABP1) is required for the recruitment of RPA (RPA32) to UV-induced DNA damage sites; depletion of hSSB2 results in decreased RPA32 phosphorylation, impaired RPA32 localization, delayed XPC recruitment to damage sites, and increased cellular sensitivity to UVB. hSSB2 levels increase after UVB irradiation and hSSB2 rapidly binds chromatin.","method":"siRNA knockdown, immunofluorescence localization, chromatin fractionation, UVB sensitivity assays","journal":"Scientific reports","confidence":"High","confidence_rationale":"Tier 2 — clean KD with defined cellular phenotype, multiple orthogonal readouts","pmids":["34642383"],"is_preprint":false},{"year":2017,"finding":"SSB1 and SSB2 (NABP1) cooperate to maintain hematopoietic stem and progenitor cell (HSPC) function; conditional double knockout causes altered replication fork dynamics, massive accumulation of DNA damage and double-strand breaks at SSB-binding regions and CpG islands, R-loop accumulation, cytosolic ssDNA accumulation, and activation of p53 and interferon pathways leading to HSPC apoptosis. Nucleotide supplementation or p53 depletion rescued the phenotype.","method":"Conditional double-knockout mouse model, replication fork dynamics assay, genome-wide DSB mapping, R-loop detection, transcriptional profiling, rescue experiments","journal":"Blood","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple orthogonal mechanistic readouts and rescue experiments","pmids":["28270450"],"is_preprint":false},{"year":2015,"finding":"Ssb2 (NABP1) knockout mice are viable and fertile with no marked phenotypic changes, and Ssb2-/- MEFs show no sensitivity to DNA-damaging agents or defects in DNA repair capacity; however, Ssb1 levels are modestly upregulated in Ssb2-/- tissues and MEFs, indicating compensatory regulation between SSB1 and SSB2.","method":"Knockout mouse model, MEF DNA damage sensitivity assays, Western blot for compensatory expression","journal":"FASEB journal","confidence":"Medium","confidence_rationale":"Tier 2 — clean KO model with defined phenotypic readouts, single lab","pmids":["25917330"],"is_preprint":false},{"year":2019,"finding":"Combined loss of SSB1 and SSB2 (NABP1) in B cell precursors causes increased ssDNA exposure, disruption of genome fragile sites, inefficient cell cycle progression, and increased DNA damage; this phenotype could be rescued by ectopic expression of either SSB1 or SSB2, but not by SSB1 ssDNA-binding mutants, and was attenuated by BCL2-mediated suppression of apoptosis.","method":"Double-knockout mouse model, B cell development assays, ssDNA detection, rescue with WT and mutant expression constructs, BCL2 overexpression","journal":"Journal of immunology","confidence":"High","confidence_rationale":"Tier 2 — genetic KO with multiple rescue conditions and orthogonal mechanistic readouts","pmids":["31085591"],"is_preprint":false},{"year":2024,"finding":"hSSB2 (NABP1) forms liquid-liquid phase separation (LLPS) condensates under physiologically relevant ionic conditions; its C-terminal intrinsically disordered region (IDR) is essential for condensate formation, and ssDNA binding is required for and facilitates phase separation. Various genome metabolic proteins are selectively enriched in hSSB2 condensates.","method":"In vitro LLPS assays, IDR deletion mutants, protein enrichment analysis in condensates","journal":"Protein science","confidence":"Medium","confidence_rationale":"Tier 1-2 — reconstituted in vitro LLPS with mutagenesis, single lab","pmids":["38511671"],"is_preprint":false},{"year":2025,"finding":"ZC3H13-mediated m6A modification stabilizes NABP1 mRNA in an IGF2BP1-dependent manner; ZC3H13 knockdown reduces NABP1 expression and attenuates G2/M cell cycle arrest and apoptosis in cisplatin-treated renal tubular cells, while ZC3H13 overexpression increases NABP1 expression and promotes cell cycle arrest and apoptosis.","method":"siRNA knockdown and overexpression, MeRIP for m6A detection, mRNA stability assay, AAV9-mediated silencing in mouse model","journal":"Cellular and molecular life sciences","confidence":"Medium","confidence_rationale":"Tier 2 — direct m6A writer-reader-target identification with functional knockdown/overexpression, in vitro and in vivo","pmids":["39985591"],"is_preprint":false}],"current_model":"NABP1 (hSSB2/OBFC2A) is a nuclear single-stranded DNA-binding protein whose OB-fold domain engages ssDNA and UV-induced CPD lesions via four key aromatic residues (W59, Y78, W82, Y89), with its C-terminal intrinsically disordered region driving multimerization on ssDNA, protein-protein interactions, and liquid-liquid phase separation; it functions in nucleotide excision repair by recruiting RPA and XPC to UV damage sites, and cooperates with SSB1 to resolve replicative stress and maintain genomic stability in hematopoietic and B cell precursors; its mRNA is stabilized by ZC3H13-mediated m6A modification read by IGF2BP1, linking it to cisplatin-induced cell cycle arrest and apoptosis."},"narrative":{"teleology":[{"year":2006,"claim":"Establishing NABP1 as a nuclear ssDNA-binding protein resolved its basic biochemical identity: it contains an OB-fold, resides in the nucleus within a high-molecular-mass complex, and preferentially binds single-stranded nucleic acids.","evidence":"Confocal microscopy, size-exclusion chromatography, and nucleic acid binding assays in human cells","pmids":["16533169"],"confidence":"Medium","gaps":["Identity of high-molecular-mass complex partners unknown","No functional assay linking ssDNA binding to a cellular process"]},{"year":2015,"claim":"Biochemical dissection showed that the C-terminal tail is required for high-affinity ssDNA binding and multimerization, distinguishing NABP1 from NABP2 in substrate preference; meanwhile, single Ssb2-knockout mice revealed functional redundancy with SSB1 in DNA repair.","evidence":"EMSA, ITC, sucrose gradient centrifugation, and Ssb2 knockout mouse model with DNA damage sensitivity assays","pmids":["26550690","25917330"],"confidence":"High","gaps":["Whether C-terminal tail mediates protein-protein interactions in vivo was untested","Extent of SSB1 compensation was not quantitatively defined"]},{"year":2017,"claim":"NMR mapping identified the ssDNA-binding interface on the OB domain, and double-knockout studies demonstrated that SSB1 and SSB2 cooperate non-redundantly in hematopoietic stem cells to protect replication forks and prevent catastrophic DNA damage.","evidence":"NMR chemical shift perturbation mapping; conditional SSB1/SSB2 double-knockout mice with replication fork dynamics, genome-wide DSB mapping, R-loop detection, and p53 rescue","pmids":["29063999","28270450"],"confidence":"High","gaps":["Structural basis of OB-fold specificity versus SSB1 not resolved at atomic level","Mechanism by which loss of SSBs leads to R-loop accumulation was unclear"]},{"year":2019,"claim":"The OB domain was shown to directly recognize UV-induced CPD lesions via the same four aromatic residues used for ssDNA binding, providing a structural rationale for NABP1's role in UV damage sensing; double-knockout B cell studies confirmed that ssDNA-binding activity is essential for genome protection.","evidence":"Biolayer interferometry and NMR with CPD-containing substrates; double-knockout B cell precursors with WT and mutant rescue constructs","pmids":["31443132","31085591"],"confidence":"High","gaps":["Whether CPD recognition occurs on genomic DNA in vivo was not shown","Structural model of OB-fold bound to CPD-containing ssDNA was not determined"]},{"year":2021,"claim":"Placing NABP1 upstream of RPA and XPC in the nucleotide excision repair pathway answered how UV damage recognition translates to repair factor loading: NABP1 depletion impaired RPA32 phosphorylation and XPC recruitment, increasing UV sensitivity.","evidence":"siRNA knockdown in human cells with immunofluorescence, chromatin fractionation, and UVB sensitivity assays","pmids":["34642383"],"confidence":"High","gaps":["Whether NABP1 directly hands off ssDNA to RPA or acts through an intermediary is unknown","Relationship between NABP1's CPD binding and RPA recruitment was not mechanistically connected"]},{"year":2024,"claim":"Discovery that NABP1 undergoes liquid-liquid phase separation via its C-terminal IDR provided a biophysical framework for how it concentrates genome-maintenance factors at damage sites.","evidence":"In vitro LLPS reconstitution with IDR deletion mutants and protein enrichment analysis","pmids":["38511671"],"confidence":"Medium","gaps":["LLPS not demonstrated in cells or at DNA damage foci","Functional consequence of phase separation for repair efficiency untested","Single-lab observation awaiting independent confirmation"]},{"year":2025,"claim":"Identification of ZC3H13-mediated m6A modification as a stabilizer of NABP1 mRNA linked epitranscriptomic regulation to NABP1's role in cisplatin-induced cell cycle arrest and apoptosis in renal tubular cells.","evidence":"MeRIP, mRNA stability assays, ZC3H13 knockdown/overexpression, and AAV9-mediated silencing in mouse kidneys","pmids":["39985591"],"confidence":"Medium","gaps":["Whether m6A-mediated regulation of NABP1 operates in other DNA-damage contexts is unknown","Direct link between NABP1 protein level changes and cisplatin repair outcomes not established"]},{"year":null,"claim":"Key unresolved questions include whether NABP1 phase condensates form at DNA damage sites in vivo, the atomic-resolution structure of the OB-fold bound to CPD-containing ssDNA, and the mechanism by which NABP1 hands off damaged substrates to RPA during NER.","evidence":"","pmids":[],"confidence":"Low","gaps":["No in vivo LLPS imaging at damage foci","No high-resolution co-crystal or cryo-EM structure with CPD substrate","Hand-off mechanism from NABP1 to RPA is entirely uncharacterized"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,1,2,3]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,4]},{"term_id":"GO:0005694","term_label":"chromosome","supporting_discovery_ids":[4]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[3,4,5,7]},{"term_id":"R-HSA-1640170","term_label":"Cell Cycle","supporting_discovery_ids":[5,7,9]}],"complexes":[],"partners":["NABP2","RPA2","XPC","ZC3H13","IGF2BP1"],"other_free_text":[]},"mechanistic_narrative":"NABP1 (hSSB2/OBFC2A) is a nuclear single-stranded DNA-binding protein that safeguards genomic integrity during replication stress and UV-induced DNA damage. Its N-terminal OB-fold domain engages ssDNA and cyclobutane pyrimidine dimers through four key aromatic residues (W59, Y78, W82, Y89), while its C-terminal intrinsically disordered region drives multimerization on ssDNA and liquid-liquid phase separation that concentrates genome-maintenance factors [PMID:26550690, PMID:31443132, PMID:38511671]. In the nucleotide excision repair pathway, NABP1 is rapidly recruited to chromatin after UV irradiation and is required for RPA and XPC accumulation at damage sites [PMID:34642383]. NABP1 acts redundantly with its paralog SSB1 (NABP2) to protect replication forks and CpG-island integrity; combined loss in hematopoietic and B cell precursors causes massive DNA breakage, R-loop accumulation, and p53-dependent apoptosis [PMID:28270450, PMID:31085591]."},"prefetch_data":{"uniprot":{"accession":"Q96AH0","full_name":"SOSS complex subunit B2","aliases":["Nucleic acid-binding protein 1","Oligonucleotide/oligosaccharide-binding fold-containing protein 2A","Sensor of single-strand DNA complex subunit B2","Sensor of ssDNA subunit B2","SOSS-B2","Single-stranded DNA-binding protein 2","hSSB2"],"length_aa":204,"mass_kda":22.4,"function":"Component of the SOSS complex, a multiprotein complex that functions downstream of the MRN complex to promote DNA repair and G2/M checkpoint. In the SOSS complex, acts as a sensor of single-stranded DNA that binds to single-stranded DNA, in particular to polypyrimidines. The SOSS complex associates with DNA lesions and influences diverse endpoints in the cellular DNA damage response including cell-cycle checkpoint activation, recombinational repair and maintenance of genomic stability. Required for efficient homologous recombination-dependent repair of double-strand breaks (DSBs) and ATM-dependent signaling pathways","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q96AH0/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/NABP1","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":[],"url":"https://opencell.sf.czbiohub.org/search/NABP1","total_profiled":1310},"omim":[{"mim_id":"612103","title":"NUCLEIC ACID-BINDING PROTEIN 1; NABP1","url":"https://www.omim.org/entry/612103"},{"mim_id":"117650","title":"CEREBROCOSTOMANDIBULAR SYNDROME; CCMS","url":"https://www.omim.org/entry/117650"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in many","driving_tissues":[],"url":"https://www.proteinatlas.org/search/NABP1"},"hgnc":{"alias_symbol":["FLJ22833","DKFZp667M1322","FLJ13624","MGC111163","SSB2","hSSB2","SOSS-B2"],"prev_symbol":["OBFC2A","NABP1-OT1"]},"alphafold":{"accession":"Q96AH0","domains":[{"cath_id":"2.40.50.140","chopping":"2-110","consensus_level":"medium","plddt":94.9962,"start":2,"end":110}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96AH0","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q96AH0-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q96AH0-F1-predicted_aligned_error_v6.png","plddt_mean":73.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=NABP1","jax_strain_url":"https://www.jax.org/strain/search?query=NABP1"},"sequence":{"accession":"Q96AH0","fasta_url":"https://rest.uniprot.org/uniprotkb/Q96AH0.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q96AH0/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q96AH0"}},"corpus_meta":[{"pmid":"16369487","id":"PMC_16369487","title":"The SPRY domain of SSB-2 adopts a novel fold that presents conserved Par-4-binding residues.","date":"2005","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/16369487","citation_count":64,"is_preprint":false},{"pmid":"15220335","id":"PMC_15220335","title":"The Reg1-interacting proteins, Bmh1, Bmh2, Ssb1, and Ssb2, have roles in maintaining glucose repression in Saccharomyces cerevisiae.","date":"2004","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/15220335","citation_count":53,"is_preprint":false},{"pmid":"16533169","id":"PMC_16533169","title":"NABP1, a novel RORgamma-regulated gene encoding a single-stranded nucleic-acid-binding protein.","date":"2006","source":"The Biochemical journal","url":"https://pubmed.ncbi.nlm.nih.gov/16533169","citation_count":25,"is_preprint":false},{"pmid":"28270450","id":"PMC_28270450","title":"Ssb1 and Ssb2 cooperate to regulate mouse hematopoietic stem and progenitor cells by resolving replicative stress.","date":"2017","source":"Blood","url":"https://pubmed.ncbi.nlm.nih.gov/28270450","citation_count":18,"is_preprint":false},{"pmid":"15964819","id":"PMC_15964819","title":"Genetic deletion of murine SPRY domain-containing SOCS box protein 2 (SSB-2) results in very mild thrombocytopenia.","date":"2005","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/15964819","citation_count":15,"is_preprint":false},{"pmid":"25917330","id":"PMC_25917330","title":"Ssb2/Nabp1 is dispensable for thymic maturation, male fertility, and DNA repair in mice.","date":"2015","source":"FASEB journal : official publication of the Federation of American Societies for Experimental Biology","url":"https://pubmed.ncbi.nlm.nih.gov/25917330","citation_count":13,"is_preprint":false},{"pmid":"31443132","id":"PMC_31443132","title":"The structural details of the interaction of single-stranded DNA binding protein hSSB2 (NABP1/OBFC2A) with UV-damaged DNA.","date":"2019","source":"Proteins","url":"https://pubmed.ncbi.nlm.nih.gov/31443132","citation_count":10,"is_preprint":false},{"pmid":"35925893","id":"PMC_35925893","title":"Arabidopsis mitochondrial single-stranded DNA-binding proteins SSB1 and SSB2 are essential regulators of mtDNA replication and homologous recombination.","date":"2022","source":"Journal of integrative plant biology","url":"https://pubmed.ncbi.nlm.nih.gov/35925893","citation_count":9,"is_preprint":false},{"pmid":"26550690","id":"PMC_26550690","title":"C-termini are essential and distinct for nucleic acid binding of human NABP1 and NABP2.","date":"2015","source":"Biochimica et biophysica acta","url":"https://pubmed.ncbi.nlm.nih.gov/26550690","citation_count":8,"is_preprint":false},{"pmid":"27793000","id":"PMC_27793000","title":"DIRC3 and near NABP1 genetic polymorphisms are associated laryngeal squamous cell carcinoma patient survival.","date":"2016","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/27793000","citation_count":7,"is_preprint":false},{"pmid":"34642383","id":"PMC_34642383","title":"hSSB2 (NABP1) is required for the recruitment of RPA during the cellular response to DNA UV damage.","date":"2021","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/34642383","citation_count":7,"is_preprint":false},{"pmid":"31085591","id":"PMC_31085591","title":"SSB1/SSB2 Proteins Safeguard B Cell Development by Protecting the Genomes of B Cell Precursors.","date":"2019","source":"Journal of immunology (Baltimore, Md. : 1950)","url":"https://pubmed.ncbi.nlm.nih.gov/31085591","citation_count":6,"is_preprint":false},{"pmid":"39985591","id":"PMC_39985591","title":"The inhibition of ZC3H13 attenuates G2/M arrest and apoptosis by alleviating NABP1 m6A modification in cisplatin-induced acute kidney injury.","date":"2025","source":"Cellular and molecular life sciences : CMLS","url":"https://pubmed.ncbi.nlm.nih.gov/39985591","citation_count":4,"is_preprint":false},{"pmid":"30382435","id":"PMC_30382435","title":"Yeast molecular chaperone gene SSB2 is involved in the endoplasmic reticulum stress response.","date":"2018","source":"Antonie van Leeuwenhoek","url":"https://pubmed.ncbi.nlm.nih.gov/30382435","citation_count":3,"is_preprint":false},{"pmid":"19621631","id":"PMC_19621631","title":"Novel ssDNA-binding properties of SSB2 and SSB3 from Thermoanaerobacter tengcongensis.","date":"2009","source":"Wei sheng wu xue bao = Acta microbiologica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/19621631","citation_count":3,"is_preprint":false},{"pmid":"38511671","id":"PMC_38511671","title":"DNA-dependent phase separation by human SSB2 (NABP1/OBFC2A) protein points to adaptations to eukaryotic genome repair processes.","date":"2024","source":"Protein science : a publication of the Protein Society","url":"https://pubmed.ncbi.nlm.nih.gov/38511671","citation_count":3,"is_preprint":false},{"pmid":"29063999","id":"PMC_29063999","title":"Backbone 1H, 13C and 15N resonance assignments of the OB domain of the single stranded DNA-binding protein hSSB2 (NABP1/OBFC2A) and chemical shift mapping of the DNA-binding interface.","date":"2017","source":"Biomolecular NMR assignments","url":"https://pubmed.ncbi.nlm.nih.gov/29063999","citation_count":3,"is_preprint":false},{"pmid":"40041566","id":"PMC_40041566","title":"The evolutionarily diverged single-stranded DNA-binding proteins SSB1/SSB2 differentially affect the replication, recombination and mutation of organellar genomes in Arabidopsis thaliana.","date":"2024","source":"Plant diversity","url":"https://pubmed.ncbi.nlm.nih.gov/40041566","citation_count":2,"is_preprint":false},{"pmid":"30039896","id":"PMC_30039896","title":"Ssb2 is a novel factor in regulating synthesis and degradation of Gcn4 in Saccharomyces cerevisiae.","date":"2018","source":"Molecular microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/30039896","citation_count":1,"is_preprint":false},{"pmid":"41078542","id":"PMC_41078542","title":"In Saccharomyces cerevisiae, the molecular chaperone proteins Ssb1 and Ssb2 upregulate ABC transporter genes, and their upregulation may play a role in the release of quorum-sensing molecules that induce cell growth arrest during the diauxic shift.","date":"2025","source":"AIMS microbiology","url":"https://pubmed.ncbi.nlm.nih.gov/41078542","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":11324,"output_tokens":2506,"usd":0.035781},"stage2":{"model":"claude-opus-4-6","input_tokens":5813,"output_tokens":2036,"usd":0.119947},"total_usd":0.155728,"stage1_batch_id":"msgbatch_012ZiiCUBfB62NCTQd4Bk1Jo","stage2_batch_id":"msgbatch_01Xuqq9aUHoQouS7UVGZNStZ","note":"batch pricing = 50% of standard"},"stage1_raw":"```json\n{\n  \"discoveries\": [\n    {\n      \"year\": 2006,\n      \"finding\": \"NABP1 (nucleic acid binding protein 1) contains an OB (oligonucleotide/oligosaccharide binding) motif at its N-terminus, localizes to the nucleus as shown by confocal microscopy, is part of a high molecular-mass nuclear protein complex as determined by size-exclusion chromatography, and binds single-stranded nucleic acids but not double-stranded DNA in direct binding assays.\",\n      \"method\": \"Confocal microscopy, size-exclusion chromatography, nucleic acid binding assays\",\n      \"journal\": \"The Biochemical journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct localization and binding experiments with functional consequence, single lab\",\n      \"pmids\": [\"16533169\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"The C-terminal tail of NABP1 (hSSB2) is essential for its DNA binding functionality; deletion of the C-terminal tail reduces ssDNA binding affinity, and the C-terminal tail is responsible for NABP1 multimerization on ssDNA. Both NABP1 and NABP2 exist as monomers in solution and prefer ssDNA over dsDNA, but NABP1 has higher affinity for ssDNA than NABP2, whereas NABP2 has higher affinity for ssRNA than NABP1.\",\n      \"method\": \"EMSA, ITC, sucrose gradient centrifugation, circular dichroism spectroscopy\",\n      \"journal\": \"Biochimica et biophysica acta\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — multiple orthogonal in vitro biochemical assays with deletion mutagenesis in a single study\",\n      \"pmids\": [\"26550690\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"NMR backbone resonance assignments of the OB domain of hSSB2 (NABP1) mapped the ssDNA interaction interface, revealing that ssDNA binding is driven by four key aromatic residues, analogous to hSSB1, though with significant differences in chemical shift perturbations reflecting differences in ssDNA recognition.\",\n      \"method\": \"NMR solution-state spectroscopy, chemical shift perturbation mapping\",\n      \"journal\": \"Biomolecular NMR assignments\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 — NMR structural mapping, single lab\",\n      \"pmids\": [\"29063999\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"The OB domain of hSSB2 (NABP1) recognizes cyclobutane pyrimidine dimers (CPDs) in ssDNA; four key aromatic residues (W59, Y78, W82, Y89) are responsible for ssDNA/CPD recognition as determined by NMR chemical shift mapping and biolayer interferometry. hSSB2 also binds duplex DNA with a two-base mismatch mimicking a CPD.\",\n      \"method\": \"Biolayer interferometry, NMR chemical shift mapping, mutagenesis\",\n      \"journal\": \"Proteins\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 — structural NMR plus biophysical binding assays with identified residues, single lab with multiple orthogonal methods\",\n      \"pmids\": [\"31443132\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"hSSB2 (NABP1) is required for the recruitment of RPA (RPA32) to UV-induced DNA damage sites; depletion of hSSB2 results in decreased RPA32 phosphorylation, impaired RPA32 localization, delayed XPC recruitment to damage sites, and increased cellular sensitivity to UVB. hSSB2 levels increase after UVB irradiation and hSSB2 rapidly binds chromatin.\",\n      \"method\": \"siRNA knockdown, immunofluorescence localization, chromatin fractionation, UVB sensitivity assays\",\n      \"journal\": \"Scientific reports\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — clean KD with defined cellular phenotype, multiple orthogonal readouts\",\n      \"pmids\": [\"34642383\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"SSB1 and SSB2 (NABP1) cooperate to maintain hematopoietic stem and progenitor cell (HSPC) function; conditional double knockout causes altered replication fork dynamics, massive accumulation of DNA damage and double-strand breaks at SSB-binding regions and CpG islands, R-loop accumulation, cytosolic ssDNA accumulation, and activation of p53 and interferon pathways leading to HSPC apoptosis. Nucleotide supplementation or p53 depletion rescued the phenotype.\",\n      \"method\": \"Conditional double-knockout mouse model, replication fork dynamics assay, genome-wide DSB mapping, R-loop detection, transcriptional profiling, rescue experiments\",\n      \"journal\": \"Blood\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple orthogonal mechanistic readouts and rescue experiments\",\n      \"pmids\": [\"28270450\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Ssb2 (NABP1) knockout mice are viable and fertile with no marked phenotypic changes, and Ssb2-/- MEFs show no sensitivity to DNA-damaging agents or defects in DNA repair capacity; however, Ssb1 levels are modestly upregulated in Ssb2-/- tissues and MEFs, indicating compensatory regulation between SSB1 and SSB2.\",\n      \"method\": \"Knockout mouse model, MEF DNA damage sensitivity assays, Western blot for compensatory expression\",\n      \"journal\": \"FASEB journal\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — clean KO model with defined phenotypic readouts, single lab\",\n      \"pmids\": [\"25917330\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Combined loss of SSB1 and SSB2 (NABP1) in B cell precursors causes increased ssDNA exposure, disruption of genome fragile sites, inefficient cell cycle progression, and increased DNA damage; this phenotype could be rescued by ectopic expression of either SSB1 or SSB2, but not by SSB1 ssDNA-binding mutants, and was attenuated by BCL2-mediated suppression of apoptosis.\",\n      \"method\": \"Double-knockout mouse model, B cell development assays, ssDNA detection, rescue with WT and mutant expression constructs, BCL2 overexpression\",\n      \"journal\": \"Journal of immunology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 — genetic KO with multiple rescue conditions and orthogonal mechanistic readouts\",\n      \"pmids\": [\"31085591\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"hSSB2 (NABP1) forms liquid-liquid phase separation (LLPS) condensates under physiologically relevant ionic conditions; its C-terminal intrinsically disordered region (IDR) is essential for condensate formation, and ssDNA binding is required for and facilitates phase separation. Various genome metabolic proteins are selectively enriched in hSSB2 condensates.\",\n      \"method\": \"In vitro LLPS assays, IDR deletion mutants, protein enrichment analysis in condensates\",\n      \"journal\": \"Protein science\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1-2 — reconstituted in vitro LLPS with mutagenesis, single lab\",\n      \"pmids\": [\"38511671\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"ZC3H13-mediated m6A modification stabilizes NABP1 mRNA in an IGF2BP1-dependent manner; ZC3H13 knockdown reduces NABP1 expression and attenuates G2/M cell cycle arrest and apoptosis in cisplatin-treated renal tubular cells, while ZC3H13 overexpression increases NABP1 expression and promotes cell cycle arrest and apoptosis.\",\n      \"method\": \"siRNA knockdown and overexpression, MeRIP for m6A detection, mRNA stability assay, AAV9-mediated silencing in mouse model\",\n      \"journal\": \"Cellular and molecular life sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 — direct m6A writer-reader-target identification with functional knockdown/overexpression, in vitro and in vivo\",\n      \"pmids\": [\"39985591\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"NABP1 (hSSB2/OBFC2A) is a nuclear single-stranded DNA-binding protein whose OB-fold domain engages ssDNA and UV-induced CPD lesions via four key aromatic residues (W59, Y78, W82, Y89), with its C-terminal intrinsically disordered region driving multimerization on ssDNA, protein-protein interactions, and liquid-liquid phase separation; it functions in nucleotide excision repair by recruiting RPA and XPC to UV damage sites, and cooperates with SSB1 to resolve replicative stress and maintain genomic stability in hematopoietic and B cell precursors; its mRNA is stabilized by ZC3H13-mediated m6A modification read by IGF2BP1, linking it to cisplatin-induced cell cycle arrest and apoptosis.\"\n}\n```","stage2_raw":"```json\n{\n  \"mechanistic_narrative\": \"NABP1 (hSSB2/OBFC2A) is a nuclear single-stranded DNA-binding protein that safeguards genomic integrity during replication stress and UV-induced DNA damage. Its N-terminal OB-fold domain engages ssDNA and cyclobutane pyrimidine dimers through four key aromatic residues (W59, Y78, W82, Y89), while its C-terminal intrinsically disordered region drives multimerization on ssDNA and liquid-liquid phase separation that concentrates genome-maintenance factors [PMID:26550690, PMID:31443132, PMID:38511671]. In the nucleotide excision repair pathway, NABP1 is rapidly recruited to chromatin after UV irradiation and is required for RPA and XPC accumulation at damage sites [PMID:34642383]. NABP1 acts redundantly with its paralog SSB1 (NABP2) to protect replication forks and CpG-island integrity; combined loss in hematopoietic and B cell precursors causes massive DNA breakage, R-loop accumulation, and p53-dependent apoptosis [PMID:28270450, PMID:31085591].\",\n  \"teleology\": [\n    {\n      \"year\": 2006,\n      \"claim\": \"Establishing NABP1 as a nuclear ssDNA-binding protein resolved its basic biochemical identity: it contains an OB-fold, resides in the nucleus within a high-molecular-mass complex, and preferentially binds single-stranded nucleic acids.\",\n      \"evidence\": \"Confocal microscopy, size-exclusion chromatography, and nucleic acid binding assays in human cells\",\n      \"pmids\": [\"16533169\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Identity of high-molecular-mass complex partners unknown\", \"No functional assay linking ssDNA binding to a cellular process\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Biochemical dissection showed that the C-terminal tail is required for high-affinity ssDNA binding and multimerization, distinguishing NABP1 from NABP2 in substrate preference; meanwhile, single Ssb2-knockout mice revealed functional redundancy with SSB1 in DNA repair.\",\n      \"evidence\": \"EMSA, ITC, sucrose gradient centrifugation, and Ssb2 knockout mouse model with DNA damage sensitivity assays\",\n      \"pmids\": [\"26550690\", \"25917330\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether C-terminal tail mediates protein-protein interactions in vivo was untested\", \"Extent of SSB1 compensation was not quantitatively defined\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"NMR mapping identified the ssDNA-binding interface on the OB domain, and double-knockout studies demonstrated that SSB1 and SSB2 cooperate non-redundantly in hematopoietic stem cells to protect replication forks and prevent catastrophic DNA damage.\",\n      \"evidence\": \"NMR chemical shift perturbation mapping; conditional SSB1/SSB2 double-knockout mice with replication fork dynamics, genome-wide DSB mapping, R-loop detection, and p53 rescue\",\n      \"pmids\": [\"29063999\", \"28270450\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of OB-fold specificity versus SSB1 not resolved at atomic level\", \"Mechanism by which loss of SSBs leads to R-loop accumulation was unclear\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"The OB domain was shown to directly recognize UV-induced CPD lesions via the same four aromatic residues used for ssDNA binding, providing a structural rationale for NABP1's role in UV damage sensing; double-knockout B cell studies confirmed that ssDNA-binding activity is essential for genome protection.\",\n      \"evidence\": \"Biolayer interferometry and NMR with CPD-containing substrates; double-knockout B cell precursors with WT and mutant rescue constructs\",\n      \"pmids\": [\"31443132\", \"31085591\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether CPD recognition occurs on genomic DNA in vivo was not shown\", \"Structural model of OB-fold bound to CPD-containing ssDNA was not determined\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Placing NABP1 upstream of RPA and XPC in the nucleotide excision repair pathway answered how UV damage recognition translates to repair factor loading: NABP1 depletion impaired RPA32 phosphorylation and XPC recruitment, increasing UV sensitivity.\",\n      \"evidence\": \"siRNA knockdown in human cells with immunofluorescence, chromatin fractionation, and UVB sensitivity assays\",\n      \"pmids\": [\"34642383\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Whether NABP1 directly hands off ssDNA to RPA or acts through an intermediary is unknown\", \"Relationship between NABP1's CPD binding and RPA recruitment was not mechanistically connected\"]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Discovery that NABP1 undergoes liquid-liquid phase separation via its C-terminal IDR provided a biophysical framework for how it concentrates genome-maintenance factors at damage sites.\",\n      \"evidence\": \"In vitro LLPS reconstitution with IDR deletion mutants and protein enrichment analysis\",\n      \"pmids\": [\"38511671\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"LLPS not demonstrated in cells or at DNA damage foci\", \"Functional consequence of phase separation for repair efficiency untested\", \"Single-lab observation awaiting independent confirmation\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Identification of ZC3H13-mediated m6A modification as a stabilizer of NABP1 mRNA linked epitranscriptomic regulation to NABP1's role in cisplatin-induced cell cycle arrest and apoptosis in renal tubular cells.\",\n      \"evidence\": \"MeRIP, mRNA stability assays, ZC3H13 knockdown/overexpression, and AAV9-mediated silencing in mouse kidneys\",\n      \"pmids\": [\"39985591\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether m6A-mediated regulation of NABP1 operates in other DNA-damage contexts is unknown\", \"Direct link between NABP1 protein level changes and cisplatin repair outcomes not established\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"Key unresolved questions include whether NABP1 phase condensates form at DNA damage sites in vivo, the atomic-resolution structure of the OB-fold bound to CPD-containing ssDNA, and the mechanism by which NABP1 hands off damaged substrates to RPA during NER.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No in vivo LLPS imaging at damage foci\", \"No high-resolution co-crystal or cryo-EM structure with CPD substrate\", \"Hand-off mechanism from NABP1 to RPA is entirely uncharacterized\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0, 1, 2, 3]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 4]},\n      {\"term_id\": \"GO:0005694\", \"supporting_discovery_ids\": [4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [3, 4, 5, 7]},\n      {\"term_id\": \"R-HSA-1640170\", \"supporting_discovery_ids\": [5, 7, 9]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"NABP2\",\n      \"RPA2\",\n      \"XPC\",\n      \"ZC3H13\",\n      \"IGF2BP1\"\n    ],\n    \"other_free_text\": []\n  }\n}\n```"}