{"gene":"POLH","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1999,"finding":"POLH encodes human DNA polymerase eta, a homologue of yeast Rad30, which belongs to the UmuC/DinB/Rev1 family of damage-bypass replication proteins. Recombinant human DNA polymerase eta directly bypasses UV-induced thymine dimers in translesion DNA synthesis, correcting the replication defect in XP-V cell extracts. All XP-V cells examined carried mutations in the POLH gene.","method":"Protein purification from HeLa cells, cell-free translesion synthesis assay, complementation of XP-V extracts with recombinant protein, mutation analysis of XP-V cell lines","journal":"Nature","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution of translesion synthesis activity, complementation assay, sequence identity to yeast Rad30, replicated across multiple XP-V cell lines","pmids":["10385124"],"is_preprint":false},{"year":1999,"finding":"The XPV-complementing protein purified from HeLa cells is a ~54 kDa monomeric DNA polymerase that replicates cyclobutane pyrimidine dimer (CPD)-containing DNA templates. Activity requires MgCl2, is sensitive to NEM, moderately sensitive to KCl, resistant to aphidicolin and ddTTP, not stimulated by PCNA, and incorporates only dATP opposite a di-thymine lesion. The monomeric 54 kDa polypeptide sediments at 3.5S.","method":"Protein purification from HeLa cells, biochemical characterization of polymerase activity, glycerol density gradient sedimentation, cell-free complementation assay with XP-V extracts","journal":"The EMBO journal","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro enzymatic assay with multiple inhibitor/cofactor conditions, sedimentation analysis, complementation across three XP-V cell strains","pmids":["10369688"],"is_preprint":false},{"year":2009,"finding":"In XP-V (POLH-deficient) cells, error-prone translesion synthesis across TT CPD lesions is carried out by a backup pathway in which DNA polymerase zeta cooperates with DNA polymerases kappa and iota. DNA polymerases zeta and kappa (but not iota) also protect XPV cells against UV cytotoxicity independently of nucleotide excision repair, establishing a genetic epistasis relationship among TLS polymerases.","method":"Genetic epistasis in XP-V patient cells, siRNA knockdown of TLS polymerases, UV cytotoxicity and mutagenesis assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — epistasis in defined genetic background (XP-V cells), two orthogonal readouts (cytotoxicity and mutagenesis), single lab","pmids":["19564618"],"is_preprint":false},{"year":2012,"finding":"Genetic interaction analysis in REV1AA Polh(-/-) double-mutant mice shows that POLH is required for the generation of C-to-G and G-to-C transversions during Ig gene somatic hypermutation that persist in REV1-catalytic-activity-deficient mice, revealing an alternative TLS pathway mediated by non-catalytic REV1 and POLH for generating these transversions.","method":"Double-mutant mouse genetics (REV1AA Polh(-/-)), Ig gene hypermutation sequencing in germinal center B cells, comparison to single mutants","journal":"International immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean genetic double-KO with defined mutation-spectrum phenotype, mechanistic epistasis established, single lab","pmids":["22223762"],"is_preprint":false},{"year":2012,"finding":"In Ung(-/-)Polh(-/-) double-mutant mice, POLH deficiency did not affect the frequency or pattern of C:G mutations during Ig gene hypermutation, and UNG deficiency did not affect A:T mutation frequency or patterns, demonstrating that UNG and POLH operate in independent, non-overlapping pathways targeting distinct U:G lesions generated at different cell cycle phases.","method":"Double-mutant mouse genetics (Ung(-/-)Polh(-/-)), Ig gene hypermutation sequencing, comparison to single mutants","journal":"Molecular immunology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic epistasis with double-KO mice and defined mutation spectrum, single lab","pmids":["22960197"],"is_preprint":false},{"year":2015,"finding":"POLH deficiency in mice causes obesity, visceral fat accumulation, hepatic steatosis, hyperinsulinemia, and glucose intolerance associated with increased DNA damage and cellular senescence (elevated ATM, γH2AX, PARP-1, p53, p16Ink4a, p21, SA-β-gal) in adipose tissue. Pharmacological inhibition of p53 with pifithrin-α reduced adipocyte senescence and attenuated metabolic abnormalities, placing POLH upstream of p53-mediated adipocyte senescence.","method":"Pol η knockout mice, metabolic phenotyping, DNA damage markers (immunostaining, western blot), pharmacological rescue with p53 inhibitor pifithrin-α, antioxidant treatment (NAC, metformin)","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — clean KO mouse model with defined metabolic and cellular phenotype, pharmacological rescue establishing pathway position, single lab","pmids":["26240351"],"is_preprint":false},{"year":2019,"finding":"Alternative polyadenylation (APA) of POLH produces three major transcripts with different 3'UTR lengths (427, 2516, and 6245 nt). The short 427-nt 3'UTR transcript escapes miR-619-mediated repression and is responsible for high POLH protein expression in cisplatin-resistant cancer cells. Loss of the short transcript sensitizes cells to cisplatin.","method":"3'UTR reporter assays, miRNA overexpression, APA site mapping, siRNA knockdown, cisplatin sensitivity assays in lung and bladder cancer cell lines","journal":"Cancer research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (reporter assay, knockdown, miRNA perturbation, drug sensitivity), single lab","pmids":["31064846"],"is_preprint":false},{"year":2021,"finding":"X-ray crystal structures of small drug-like fragment compounds bound to POLH were solved (first reported crystal structures with bound inhibitors), enabling identification of binding sites on the polymerase as starting points for inhibitor development. Medicinal chemistry optimization produced inhibitors with functional activity in an in vitro biochemical assay.","method":"Fragment-based drug discovery, X-ray crystallography of POLH with bound fragments, in vitro biochemical polymerase inhibition assay","journal":"Frontiers in oncology","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — crystal structures with bound ligands and biochemical assay validation, but single study and focused on inhibitor discovery rather than mechanism","pmids":["34900730"],"is_preprint":false},{"year":2023,"finding":"Three POLH germline missense variants (C34W, I147N, R167Q) showed 4- to 14-fold reductions in specificity constants (kcat/Km) for dATP insertion opposite CTD lesions and failed to rescue UV- and cisplatin-sensitivity in POLH-knockout cells, identifying these as functionally defective variants. Two XPV-pathogenic mutants (R93P, G263V) and an active-site double mutant (D115A/E116A) also failed to rescue, validating the assay system.","method":"Recombinant protein expression, steady-state kinetics with CTD-containing templates, CRISPR/Cas9 POLH-knockout cell complementation assay, UV and cisplatin sensitivity assays","journal":"International journal of molecular sciences","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro enzymatic kinetics with mutagenesis combined with cell-based complementation, single lab with two orthogonal methods","pmids":["36982269"],"is_preprint":false},{"year":2025,"finding":"Four POLH germline variants (R81C, F17S, C227Y, R356X) impair pol η function: F17S, C227Y, and R356X showed 3- to 5000-fold reductions in kcat/Km for dATP insertion opposite CTD in vitro; R81C protein was undetectable in transfected cells (protein instability). CRISPR knock-in of R81C caused reduced pol η protein expression and increased cisplatin sensitivity. All four variants failed to rescue UV- and cisplatin-sensitivity in POLH-deficient cells.","method":"Recombinant protein kinetics, CRISPR/Cas9 knock-in and knockout in HEK293T cells, complementation assay, western blot, UV and cisplatin sensitivity assays","journal":"Chemico-biological interactions","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro steady-state kinetics with multiple variants combined with CRISPR knock-in cell model, single lab","pmids":["40334807"],"is_preprint":false},{"year":2014,"finding":"Site-directed mutagenesis of POLH at Y52E reduced the capacity of pol η to bypass UV-induced CPD lesions in HaCaT keratinocytes, as measured by slower CPD clearance and lower cell viability recovery after UVB irradiation compared to wild-type POLH.","method":"Site-directed mutagenesis (Y52E), transfection into HaCaT cells, CPD immunodetection, MTT cell viability assay","journal":"The West Indian medical journal","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single-point mutagenesis with cell-based readout, single lab, limited mechanistic resolution","pmids":["25429473"],"is_preprint":false},{"year":2025,"finding":"In Drosophila, PolH (ortholog of human POLH) and Rev1 are interacting partners that localize to active LTR-retrotransposons and safeguard RNA Polymerase II occupancy at these loci, promoting their transcription. Rev1 associates with RNA Pol II as shown by mass spectrometry and proximity ligation assay; CUT&Tag shows enrichment of PolH at LTR-retrotransposons.","method":"Genetic screen in Drosophila, CUT&Tag, mass spectrometry, proximity ligation assay, RNA Pol II ChIP-sequencing","journal":"Nucleic acids research","confidence":"Low","confidence_rationale":"Tier 2 / Weak — multiple orthogonal methods but findings are in Drosophila and describe a non-canonical (transcriptional) role not replicated in mammalian systems","pmids":["40966519"],"is_preprint":false}],"current_model":"POLH encodes human DNA polymerase eta, a Y-family translesion synthesis polymerase that accurately bypasses UV-induced cyclobutane pyrimidine dimers (incorporating dATP opposite di-thymine lesions) and cisplatin-induced intrastrand crosslinks; loss of POLH function causes xeroderma pigmentosum variant (XP-V), and in its absence backup error-prone TLS is carried out by a pathway involving polymerases zeta, kappa, and iota. POLH also contributes to A:T mutagenesis during Ig gene somatic hypermutation through an independent pathway from UNG, and its expression is post-transcriptionally regulated by alternative polyadenylation and miR-619, with the short 3'UTR isoform conferring cisplatin resistance."},"narrative":{"mechanistic_narrative":"POLH encodes human DNA polymerase eta, a damage-bypass replication enzyme of the UmuC/DinB/Rev1 family that performs translesion synthesis (TLS) past UV-induced lesions; loss of POLH function underlies xeroderma pigmentosum variant (XP-V), and all XP-V cells examined carry POLH mutations [PMID:10385124]. The purified ~54 kDa monomeric polymerase replicates cyclobutane pyrimidine dimer (CPD)-containing templates, requires Mg2+, is aphidicolin- and ddTTP-resistant, and accurately inserts dATP opposite a di-thymine lesion, accounting for its error-free bypass of UV photoproducts [PMID:10369688]. When POLH is absent, error-prone backup TLS across TT CPDs is carried out by DNA polymerase zeta cooperating with polymerases kappa and iota, with zeta and kappa additionally protecting cells from UV cytotoxicity independently of nucleotide excision repair [PMID:19564618]. Beyond UV photoproducts, pol eta bypasses cisplatin lesions, and germline missense variants that reduce its catalytic efficiency (kcat/Km for dATP insertion opposite CTD lesions) or destabilize the protein fail to rescue UV- and cisplatin-sensitivity in POLH-deficient cells [PMID:36982269, PMID:40334807]. POLH also has roles beyond replicative lesion bypass: it generates A:T and C-to-G/G-to-C transversions during immunoglobulin somatic hypermutation through a pathway involving non-catalytic REV1 and operating independently of UNG [PMID:22223762, PMID:22960197], and POLH-deficient mice develop a metabolic syndrome driven by DNA-damage-associated, p53-dependent adipocyte senescence [PMID:26240351]. POLH expression is post-transcriptionally controlled by alternative polyadenylation, with a short 3'UTR isoform escaping miR-619 repression to drive high pol eta levels and cisplatin resistance in cancer cells [PMID:31064846].","teleology":[{"year":1999,"claim":"Established that the gene defective in XP-V encodes a translesion polymerase, answering why XP-V cells cannot replicate UV-damaged DNA.","evidence":"Purification of a ~54 kDa monomeric polymerase from HeLa cells, cell-free TLS assay, complementation of XP-V extracts, and POLH mutation analysis across XP-V lines","pmids":["10385124","10369688"],"confidence":"High","gaps":["Structural basis of accurate di-thymine bypass not resolved at atomic level","Regulation of recruitment to replication forks not addressed"]},{"year":2009,"claim":"Defined the backup machinery that operates when pol eta is missing, explaining the error-prone, mutagenic outcome of UV bypass in XP-V cells.","evidence":"Genetic epistasis with siRNA knockdown of TLS polymerases in XP-V patient cells, with cytotoxicity and mutagenesis readouts","pmids":["19564618"],"confidence":"Medium","gaps":["Single lab","Biochemical division of labor between zeta, kappa, and iota not reconstituted"]},{"year":2012,"claim":"Showed POLH contributes to antibody diversification through pathways distinct from its replicative TLS role, broadening its physiological function.","evidence":"REV1AA Polh(-/-) and Ung(-/-)Polh(-/-) double-mutant mouse genetics with Ig gene hypermutation spectrum sequencing","pmids":["22223762","22960197"],"confidence":"Medium","gaps":["Molecular basis of REV1–POLH cooperation for transversions undefined","Single lab"]},{"year":2015,"claim":"Linked POLH loss to a systemic phenotype, placing the polymerase upstream of p53-dependent cellular senescence in metabolic tissue.","evidence":"Pol eta knockout mice with metabolic phenotyping, DNA-damage/senescence markers, and pharmacological p53 inhibition rescue","pmids":["26240351"],"confidence":"Medium","gaps":["Tissue-specific lesion driving senescence not identified","Single lab"]},{"year":2019,"claim":"Identified post-transcriptional control of POLH expression as a determinant of chemoresistance.","evidence":"APA site mapping, 3'UTR reporter assays, miR-619 perturbation, and cisplatin sensitivity assays in cancer cell lines","pmids":["31064846"],"confidence":"Medium","gaps":["Upstream regulation of APA choice unknown","Single lab"]},{"year":2023,"claim":"Built a functional assay framework distinguishing pathogenic from benign POLH variants by coupling kinetics to cellular rescue.","evidence":"Recombinant kinetics on CTD templates plus CRISPR knockout complementation with UV/cisplatin sensitivity in 2023 and 2025 studies","pmids":["36982269","40334807"],"confidence":"Medium","gaps":["Genotype–phenotype mapping to XP-V severity incomplete","Protein-stability versus catalytic mechanisms not always separable","Single lab"]},{"year":2021,"claim":"Provided the first liganded POLH crystal structures, opening structure-guided inhibitor development against the polymerase.","evidence":"Fragment-based drug discovery with X-ray crystallography and in vitro biochemical inhibition assays","pmids":["34900730"],"confidence":"Medium","gaps":["Inhibitor specificity over other Y-family polymerases not established","Cellular efficacy not demonstrated"]},{"year":2025,"claim":"Raised a non-canonical transcriptional role for the POLH ortholog at retrotransposons, distinct from replicative lesion bypass.","evidence":"Drosophila genetic screen, CUT&Tag, mass spectrometry, proximity ligation, and RNA Pol II ChIP-seq","pmids":["40966519"],"confidence":"Low","gaps":["Findings in Drosophila, not replicated in mammalian systems","Mechanistic link between PolH and RNA Pol II occupancy unresolved"]},{"year":null,"claim":"How pol eta is selectively recruited to and exchanged at sites of distinct lesion types, and whether its transcriptional/retrotransposon role exists in mammals, remain open.","evidence":"","pmids":[],"confidence":"Low","gaps":["No mammalian validation of transcriptional role","Lesion-specific polymerase switching mechanism uncharacterized in the corpus"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[0,1,8,9]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[1]},{"term_id":"GO:0016740","term_label":"transferase activity","supporting_discovery_ids":[1,8]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[0,1]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[0,1]}],"complexes":[],"partners":["REV1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9Y253","full_name":"DNA polymerase eta","aliases":["RAD30 homolog A","Xeroderma pigmentosum variant type protein"],"length_aa":713,"mass_kda":78.4,"function":"DNA polymerase specifically involved in the DNA repair by translesion synthesis (TLS) (PubMed:10385124, PubMed:11743006, PubMed:16357261, PubMed:20388628, PubMed:24449906, PubMed:24553286, PubMed:38212351). Due to low processivity on both damaged and normal DNA, cooperates with the heterotetrameric (REV3L, REV7, POLD2 and POLD3) POLZ complex for complete bypass of DNA lesions. Inserts one or 2 nucleotide(s) opposite the lesion, the primer is further extended by the tetrameric POLZ complex. In the case of 1,2-intrastrand d(GpG)-cisplatin cross-link, inserts dCTP opposite the 3' guanine (PubMed:24449906). Particularly important for the repair of UV-induced pyrimidine dimers (PubMed:10385124, PubMed:11743006). Although inserts the correct base, may cause base transitions and transversions depending upon the context. May play a role in hypermutation at immunoglobulin genes (PubMed:11376341, PubMed:14734526). Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but does not have any lyase activity, preventing the release of the 5'-deoxyribose phosphate (5'-dRP) residue. This covalent trapping of the enzyme by the 5'-dRP residue inhibits its DNA synthetic activity during base excision repair, thereby avoiding high incidence of mutagenesis (PubMed:14630940). Targets POLI to replication foci (PubMed:12606586)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9Y253/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/POLH","classification":"Not Classified","n_dependent_lines":32,"n_total_lines":1208,"dependency_fraction":0.026490066225165563},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[],"url":"https://opencell.sf.czbiohub.org/search/POLH","total_profiled":1310},"omim":[{"mim_id":"616578","title":"ZINC FINGER- AND BTB DOMAIN-CONTAINING PROTEIN 1; ZBTB1","url":"https://www.omim.org/entry/616578"},{"mim_id":"616086","title":"SprT-LIKE N-TERMINAL DOMAIN PROTEIN; SPRTN","url":"https://www.omim.org/entry/616086"},{"mim_id":"609534","title":"ATPase FAMILY, AAA DOMAIN-CONTAINING, MEMBER 5; ATAD5","url":"https://www.omim.org/entry/609534"},{"mim_id":"605650","title":"POLYMERASE, DNA, KAPPA; POLK","url":"https://www.omim.org/entry/605650"},{"mim_id":"605252","title":"POLYMERASE, DNA, IOTA; POLI","url":"https://www.omim.org/entry/605252"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoplasm","reliability":"Enhanced"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POLH"},"hgnc":{"alias_symbol":["XPV","RAD30A","XP-V"],"prev_symbol":[]},"alphafold":{"accession":"Q9Y253","domains":[{"cath_id":"3.30.70.270","chopping":"8-240","consensus_level":"medium","plddt":96.5755,"start":8,"end":240},{"cath_id":"1.10.150.20","chopping":"244-314","consensus_level":"medium","plddt":97.8679,"start":244,"end":314},{"cath_id":"3.30.1490.100","chopping":"318-430","consensus_level":"high","plddt":97.6142,"start":318,"end":430}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y253","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y253-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9Y253-F1-predicted_aligned_error_v6.png","plddt_mean":76.88},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLH","jax_strain_url":"https://www.jax.org/strain/search?query=POLH"},"sequence":{"accession":"Q9Y253","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9Y253.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9Y253/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9Y253"}},"corpus_meta":[{"pmid":"10385124","id":"PMC_10385124","title":"The XPV (xeroderma pigmentosum variant) gene encodes human DNA polymerase eta.","date":"1999","source":"Nature","url":"https://pubmed.ncbi.nlm.nih.gov/10385124","citation_count":1125,"is_preprint":false},{"pmid":"10369688","id":"PMC_10369688","title":"Xeroderma pigmentosum variant (XP-V) correcting protein from HeLa cells has a thymine dimer bypass DNA polymerase activity.","date":"1999","source":"The EMBO journal","url":"https://pubmed.ncbi.nlm.nih.gov/10369688","citation_count":379,"is_preprint":false},{"pmid":"19564618","id":"PMC_19564618","title":"DNA polymerase zeta cooperates with polymerases kappa and iota in translesion DNA synthesis across pyrimidine photodimers in cells from XPV patients.","date":"2009","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/19564618","citation_count":104,"is_preprint":false},{"pmid":"26240351","id":"PMC_26240351","title":"Ablation of XP-V gene causes adipose tissue senescence and metabolic abnormalities.","date":"2015","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/26240351","citation_count":68,"is_preprint":false},{"pmid":"11032022","id":"PMC_11032022","title":"Genomic structure, chromosomal localization and identification of mutations in the xeroderma pigmentosum variant (XPV) gene.","date":"2000","source":"Oncogene","url":"https://pubmed.ncbi.nlm.nih.gov/11032022","citation_count":48,"is_preprint":false},{"pmid":"31064846","id":"PMC_31064846","title":"A PolH Transcript with a Short 3'UTR Enhances PolH Expression and Mediates Cisplatin Resistance.","date":"2019","source":"Cancer research","url":"https://pubmed.ncbi.nlm.nih.gov/31064846","citation_count":40,"is_preprint":false},{"pmid":"24929193","id":"PMC_24929193","title":"C-reactive protein and depression in persons with Human Immunodeficiency Virus infection: the Positive Living with HIV (POLH) 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Part A","url":"https://pubmed.ncbi.nlm.nih.gov/28688171","citation_count":6,"is_preprint":false},{"pmid":"35111200","id":"PMC_35111200","title":"XPC and POLH/XPV Genes Mutated in a Genetic Cluster of Xeroderma Pigmentosum Patients in Northeast Brazil.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35111200","citation_count":5,"is_preprint":false},{"pmid":"27370977","id":"PMC_27370977","title":"Dietary B Vitamins and Serum C-Reactive Protein in Persons With Human Immunodeficiency Virus Infection: The Positive Living With HIV (POLH) Study.","date":"2016","source":"Food and nutrition bulletin","url":"https://pubmed.ncbi.nlm.nih.gov/27370977","citation_count":5,"is_preprint":false},{"pmid":"36982269","id":"PMC_36982269","title":"Identification of Three Human POLH Germline Variants Defective in Complementing the UV- and Cisplatin-Sensitivity of POLH-Deficient Cells.","date":"2023","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36982269","citation_count":3,"is_preprint":false},{"pmid":"34030998","id":"PMC_34030998","title":"Xeroderma pigmentosum variant: squamous cell carcinoma of the lower lip harboring exon 11 mutation of POLH.","date":"2021","source":"Oral surgery, oral medicine, oral pathology and oral radiology","url":"https://pubmed.ncbi.nlm.nih.gov/34030998","citation_count":3,"is_preprint":false},{"pmid":"32935933","id":"PMC_32935933","title":"Novel variants in POLH and TREM2 genes associated with a complex phenotype of xeroderma pigmentosum variant type and early-onset dementia.","date":"2020","source":"Molecular genetics & genomic medicine","url":"https://pubmed.ncbi.nlm.nih.gov/32935933","citation_count":3,"is_preprint":false},{"pmid":"27313696","id":"PMC_27313696","title":"miR-20b downregulates polymerases κ and θ in XP-V tumor cells.","date":"2016","source":"Oncology letters","url":"https://pubmed.ncbi.nlm.nih.gov/27313696","citation_count":3,"is_preprint":false},{"pmid":"35062357","id":"PMC_35062357","title":"Actin Contributes to the Hyperexpression of Baculovirus Polyhedrin (polh) and p10 as a Component of Transcription Initiation Complex (TIC).","date":"2022","source":"Viruses","url":"https://pubmed.ncbi.nlm.nih.gov/35062357","citation_count":2,"is_preprint":false},{"pmid":"40966519","id":"PMC_40966519","title":"Translesion DNA polymerases Rev1 and PolH promote LTR-retrotransposon transcription by safeguarding Pol II occupancy in both germline and somatic tissues of Drosophila.","date":"2025","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/40966519","citation_count":1,"is_preprint":false},{"pmid":"35328096","id":"PMC_35328096","title":"Identification of Frameshift Variants in POLH Gene Causing Xeroderma Pigmentosum in Two Consanguineous Pakistani Families.","date":"2022","source":"Genes","url":"https://pubmed.ncbi.nlm.nih.gov/35328096","citation_count":1,"is_preprint":false},{"pmid":"14610738","id":"PMC_14610738","title":"[Establishment of a cell line with antisense-blocked POLH and the role of POLH in alkylating agent MNNG induced nontargeted mutagenesis].","date":"2003","source":"Zhejiang da xue xue bao. Yi xue ban = Journal of Zhejiang University. Medical sciences","url":"https://pubmed.ncbi.nlm.nih.gov/14610738","citation_count":1,"is_preprint":false},{"pmid":"25429473","id":"PMC_25429473","title":"Site-directed Mutagenesis (Y52E) of POLH Affects Its Ability to Bypass Ultraviolet-induced DNA Lesions in HaCaT Cells.","date":"2014","source":"The West Indian medical journal","url":"https://pubmed.ncbi.nlm.nih.gov/25429473","citation_count":1,"is_preprint":false},{"pmid":"25165004","id":"PMC_25165004","title":"Minimal detection of nuclear mutations in XP-V and normal cells treated with oxidative stress inducing agents.","date":"2014","source":"Journal of biochemical and molecular toxicology","url":"https://pubmed.ncbi.nlm.nih.gov/25165004","citation_count":1,"is_preprint":false},{"pmid":"39655645","id":"PMC_39655645","title":"Identification of novel variants of XPA and POLH/XPV genes in xeroderma pigmentosum patients in Vietnam.","date":"2024","source":"Personalized medicine","url":"https://pubmed.ncbi.nlm.nih.gov/39655645","citation_count":0,"is_preprint":false},{"pmid":"41315479","id":"PMC_41315479","title":"Germline variants of the POLH and RAD51 genes are candidate variants associated with risk of hormone receptor-negative young-onset breast cancer.","date":"2025","source":"NPJ breast cancer","url":"https://pubmed.ncbi.nlm.nih.gov/41315479","citation_count":0,"is_preprint":false},{"pmid":"40334807","id":"PMC_40334807","title":"Four germline POLH variants, including two found in skin tumors, impair DNA polymerase η function and cellular tolerance to UV radiation and cisplatin.","date":"2025","source":"Chemico-biological interactions","url":"https://pubmed.ncbi.nlm.nih.gov/40334807","citation_count":0,"is_preprint":false},{"pmid":"19069642","id":"PMC_19069642","title":"[Study on expression regularity of XPV mRNA in L-02 hepatic cells induced by hydroquinone].","date":"2008","source":"Wei sheng yan jiu = Journal of hygiene research","url":"https://pubmed.ncbi.nlm.nih.gov/19069642","citation_count":0,"is_preprint":false},{"pmid":"40769549","id":"PMC_40769549","title":"[Expression pattern of polyhedrin of BmNPV and involvement of importin α in the nuclear import of Polh].","date":"2025","source":"Sheng wu gong cheng xue bao = Chinese journal of biotechnology","url":"https://pubmed.ncbi.nlm.nih.gov/40769549","citation_count":0,"is_preprint":false},{"pmid":"35984432","id":"PMC_35984432","title":"A new POLH mutation in a consanguineous Chinese family with xeroderma pigmentosum variant type.","date":"2022","source":"Clinical and experimental dermatology","url":"https://pubmed.ncbi.nlm.nih.gov/35984432","citation_count":0,"is_preprint":false},{"pmid":"41074151","id":"PMC_41074151","title":"Identification of radiation-sensitive genes as biomarkers for biodosimetry: an ex vivo analysis of TNFRSF10B, ZMAT3, POLH, and PLK2 in human blood samples.","date":"2025","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/41074151","citation_count":0,"is_preprint":false},{"pmid":"11209691","id":"PMC_11209691","title":"[Mutagenic analysis on the polyhedrin gene (polh) of Bombyx mori nuclear polyhedrosis virus (BmNPV)].","date":"2000","source":"Yi chuan xue bao = Acta genetica Sinica","url":"https://pubmed.ncbi.nlm.nih.gov/11209691","citation_count":0,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.10.25.684582","title":"Ancestry-Aware Modeling of Dark Cyclobutane Pyrimidine Dimer Formation Integrating GTEx Skin Transcriptomes and Evolutionary Genomics","date":"2025-10-28","source":"bioRxiv","url":"https://doi.org/10.1101/2025.10.25.684582","citation_count":0,"is_preprint":true},{"pmid":null,"id":"bio_10.1101_2025.07.11.664482","title":"Epitranscriptome-wide profiling identifies RNA editing events regulated by ADAR1 that are associated with DNA repair mechanisms in human TK6 cells","date":"2025-07-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.07.11.664482","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":22259,"output_tokens":3349,"usd":0.058506,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":10945,"output_tokens":2811,"usd":0.0625,"stage2_stop_reason":"end_turn"},"total_usd":0.121006,"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\": 1999,\n      \"finding\": \"POLH encodes human DNA polymerase eta, a homologue of yeast Rad30, which belongs to the UmuC/DinB/Rev1 family of damage-bypass replication proteins. Recombinant human DNA polymerase eta directly bypasses UV-induced thymine dimers in translesion DNA synthesis, correcting the replication defect in XP-V cell extracts. All XP-V cells examined carried mutations in the POLH gene.\",\n      \"method\": \"Protein purification from HeLa cells, cell-free translesion synthesis assay, complementation of XP-V extracts with recombinant protein, mutation analysis of XP-V cell lines\",\n      \"journal\": \"Nature\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution of translesion synthesis activity, complementation assay, sequence identity to yeast Rad30, replicated across multiple XP-V cell lines\",\n      \"pmids\": [\"10385124\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"The XPV-complementing protein purified from HeLa cells is a ~54 kDa monomeric DNA polymerase that replicates cyclobutane pyrimidine dimer (CPD)-containing DNA templates. Activity requires MgCl2, is sensitive to NEM, moderately sensitive to KCl, resistant to aphidicolin and ddTTP, not stimulated by PCNA, and incorporates only dATP opposite a di-thymine lesion. The monomeric 54 kDa polypeptide sediments at 3.5S.\",\n      \"method\": \"Protein purification from HeLa cells, biochemical characterization of polymerase activity, glycerol density gradient sedimentation, cell-free complementation assay with XP-V extracts\",\n      \"journal\": \"The EMBO journal\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro enzymatic assay with multiple inhibitor/cofactor conditions, sedimentation analysis, complementation across three XP-V cell strains\",\n      \"pmids\": [\"10369688\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"In XP-V (POLH-deficient) cells, error-prone translesion synthesis across TT CPD lesions is carried out by a backup pathway in which DNA polymerase zeta cooperates with DNA polymerases kappa and iota. DNA polymerases zeta and kappa (but not iota) also protect XPV cells against UV cytotoxicity independently of nucleotide excision repair, establishing a genetic epistasis relationship among TLS polymerases.\",\n      \"method\": \"Genetic epistasis in XP-V patient cells, siRNA knockdown of TLS polymerases, UV cytotoxicity and mutagenesis assays\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — epistasis in defined genetic background (XP-V cells), two orthogonal readouts (cytotoxicity and mutagenesis), single lab\",\n      \"pmids\": [\"19564618\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"Genetic interaction analysis in REV1AA Polh(-/-) double-mutant mice shows that POLH is required for the generation of C-to-G and G-to-C transversions during Ig gene somatic hypermutation that persist in REV1-catalytic-activity-deficient mice, revealing an alternative TLS pathway mediated by non-catalytic REV1 and POLH for generating these transversions.\",\n      \"method\": \"Double-mutant mouse genetics (REV1AA Polh(-/-)), Ig gene hypermutation sequencing in germinal center B cells, comparison to single mutants\",\n      \"journal\": \"International immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean genetic double-KO with defined mutation-spectrum phenotype, mechanistic epistasis established, single lab\",\n      \"pmids\": [\"22223762\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2012,\n      \"finding\": \"In Ung(-/-)Polh(-/-) double-mutant mice, POLH deficiency did not affect the frequency or pattern of C:G mutations during Ig gene hypermutation, and UNG deficiency did not affect A:T mutation frequency or patterns, demonstrating that UNG and POLH operate in independent, non-overlapping pathways targeting distinct U:G lesions generated at different cell cycle phases.\",\n      \"method\": \"Double-mutant mouse genetics (Ung(-/-)Polh(-/-)), Ig gene hypermutation sequencing, comparison to single mutants\",\n      \"journal\": \"Molecular immunology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic epistasis with double-KO mice and defined mutation spectrum, single lab\",\n      \"pmids\": [\"22960197\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"POLH deficiency in mice causes obesity, visceral fat accumulation, hepatic steatosis, hyperinsulinemia, and glucose intolerance associated with increased DNA damage and cellular senescence (elevated ATM, γH2AX, PARP-1, p53, p16Ink4a, p21, SA-β-gal) in adipose tissue. Pharmacological inhibition of p53 with pifithrin-α reduced adipocyte senescence and attenuated metabolic abnormalities, placing POLH upstream of p53-mediated adipocyte senescence.\",\n      \"method\": \"Pol η knockout mice, metabolic phenotyping, DNA damage markers (immunostaining, western blot), pharmacological rescue with p53 inhibitor pifithrin-α, antioxidant treatment (NAC, metformin)\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — clean KO mouse model with defined metabolic and cellular phenotype, pharmacological rescue establishing pathway position, single lab\",\n      \"pmids\": [\"26240351\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2019,\n      \"finding\": \"Alternative polyadenylation (APA) of POLH produces three major transcripts with different 3'UTR lengths (427, 2516, and 6245 nt). The short 427-nt 3'UTR transcript escapes miR-619-mediated repression and is responsible for high POLH protein expression in cisplatin-resistant cancer cells. Loss of the short transcript sensitizes cells to cisplatin.\",\n      \"method\": \"3'UTR reporter assays, miRNA overexpression, APA site mapping, siRNA knockdown, cisplatin sensitivity assays in lung and bladder cancer cell lines\",\n      \"journal\": \"Cancer research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (reporter assay, knockdown, miRNA perturbation, drug sensitivity), single lab\",\n      \"pmids\": [\"31064846\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"X-ray crystal structures of small drug-like fragment compounds bound to POLH were solved (first reported crystal structures with bound inhibitors), enabling identification of binding sites on the polymerase as starting points for inhibitor development. Medicinal chemistry optimization produced inhibitors with functional activity in an in vitro biochemical assay.\",\n      \"method\": \"Fragment-based drug discovery, X-ray crystallography of POLH with bound fragments, in vitro biochemical polymerase inhibition assay\",\n      \"journal\": \"Frontiers in oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — crystal structures with bound ligands and biochemical assay validation, but single study and focused on inhibitor discovery rather than mechanism\",\n      \"pmids\": [\"34900730\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Three POLH germline missense variants (C34W, I147N, R167Q) showed 4- to 14-fold reductions in specificity constants (kcat/Km) for dATP insertion opposite CTD lesions and failed to rescue UV- and cisplatin-sensitivity in POLH-knockout cells, identifying these as functionally defective variants. Two XPV-pathogenic mutants (R93P, G263V) and an active-site double mutant (D115A/E116A) also failed to rescue, validating the assay system.\",\n      \"method\": \"Recombinant protein expression, steady-state kinetics with CTD-containing templates, CRISPR/Cas9 POLH-knockout cell complementation assay, UV and cisplatin sensitivity assays\",\n      \"journal\": \"International journal of molecular sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro enzymatic kinetics with mutagenesis combined with cell-based complementation, single lab with two orthogonal methods\",\n      \"pmids\": [\"36982269\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"Four POLH germline variants (R81C, F17S, C227Y, R356X) impair pol η function: F17S, C227Y, and R356X showed 3- to 5000-fold reductions in kcat/Km for dATP insertion opposite CTD in vitro; R81C protein was undetectable in transfected cells (protein instability). CRISPR knock-in of R81C caused reduced pol η protein expression and increased cisplatin sensitivity. All four variants failed to rescue UV- and cisplatin-sensitivity in POLH-deficient cells.\",\n      \"method\": \"Recombinant protein kinetics, CRISPR/Cas9 knock-in and knockout in HEK293T cells, complementation assay, western blot, UV and cisplatin sensitivity assays\",\n      \"journal\": \"Chemico-biological interactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro steady-state kinetics with multiple variants combined with CRISPR knock-in cell model, single lab\",\n      \"pmids\": [\"40334807\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"Site-directed mutagenesis of POLH at Y52E reduced the capacity of pol η to bypass UV-induced CPD lesions in HaCaT keratinocytes, as measured by slower CPD clearance and lower cell viability recovery after UVB irradiation compared to wild-type POLH.\",\n      \"method\": \"Site-directed mutagenesis (Y52E), transfection into HaCaT cells, CPD immunodetection, MTT cell viability assay\",\n      \"journal\": \"The West Indian medical journal\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single-point mutagenesis with cell-based readout, single lab, limited mechanistic resolution\",\n      \"pmids\": [\"25429473\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"In Drosophila, PolH (ortholog of human POLH) and Rev1 are interacting partners that localize to active LTR-retrotransposons and safeguard RNA Polymerase II occupancy at these loci, promoting their transcription. Rev1 associates with RNA Pol II as shown by mass spectrometry and proximity ligation assay; CUT&Tag shows enrichment of PolH at LTR-retrotransposons.\",\n      \"method\": \"Genetic screen in Drosophila, CUT&Tag, mass spectrometry, proximity ligation assay, RNA Pol II ChIP-sequencing\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 2 / Weak — multiple orthogonal methods but findings are in Drosophila and describe a non-canonical (transcriptional) role not replicated in mammalian systems\",\n      \"pmids\": [\"40966519\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLH encodes human DNA polymerase eta, a Y-family translesion synthesis polymerase that accurately bypasses UV-induced cyclobutane pyrimidine dimers (incorporating dATP opposite di-thymine lesions) and cisplatin-induced intrastrand crosslinks; loss of POLH function causes xeroderma pigmentosum variant (XP-V), and in its absence backup error-prone TLS is carried out by a pathway involving polymerases zeta, kappa, and iota. POLH also contributes to A:T mutagenesis during Ig gene somatic hypermutation through an independent pathway from UNG, and its expression is post-transcriptionally regulated by alternative polyadenylation and miR-619, with the short 3'UTR isoform conferring cisplatin resistance.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLH encodes human DNA polymerase eta, a damage-bypass replication enzyme of the UmuC/DinB/Rev1 family that performs translesion synthesis (TLS) past UV-induced lesions; loss of POLH function underlies xeroderma pigmentosum variant (XP-V), and all XP-V cells examined carry POLH mutations [#0]. The purified ~54 kDa monomeric polymerase replicates cyclobutane pyrimidine dimer (CPD)-containing templates, requires Mg2+, is aphidicolin- and ddTTP-resistant, and accurately inserts dATP opposite a di-thymine lesion, accounting for its error-free bypass of UV photoproducts [#1]. When POLH is absent, error-prone backup TLS across TT CPDs is carried out by DNA polymerase zeta cooperating with polymerases kappa and iota, with zeta and kappa additionally protecting cells from UV cytotoxicity independently of nucleotide excision repair [#2]. Beyond UV photoproducts, pol eta bypasses cisplatin lesions, and germline missense variants that reduce its catalytic efficiency (kcat/Km for dATP insertion opposite CTD lesions) or destabilize the protein fail to rescue UV- and cisplatin-sensitivity in POLH-deficient cells [#8, #9]. POLH also has roles beyond replicative lesion bypass: it generates A:T and C-to-G/G-to-C transversions during immunoglobulin somatic hypermutation through a pathway involving non-catalytic REV1 and operating independently of UNG [#3, #4], and POLH-deficient mice develop a metabolic syndrome driven by DNA-damage-associated, p53-dependent adipocyte senescence [#5]. POLH expression is post-transcriptionally controlled by alternative polyadenylation, with a short 3'UTR isoform escaping miR-619 repression to drive high pol eta levels and cisplatin resistance in cancer cells [#6].\",\n  \"teleology\": [\n    {\n      \"year\": 1999,\n      \"claim\": \"Established that the gene defective in XP-V encodes a translesion polymerase, answering why XP-V cells cannot replicate UV-damaged DNA.\",\n      \"evidence\": \"Purification of a ~54 kDa monomeric polymerase from HeLa cells, cell-free TLS assay, complementation of XP-V extracts, and POLH mutation analysis across XP-V lines\",\n      \"pmids\": [\"10385124\", \"10369688\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Structural basis of accurate di-thymine bypass not resolved at atomic level\", \"Regulation of recruitment to replication forks not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Defined the backup machinery that operates when pol eta is missing, explaining the error-prone, mutagenic outcome of UV bypass in XP-V cells.\",\n      \"evidence\": \"Genetic epistasis with siRNA knockdown of TLS polymerases in XP-V patient cells, with cytotoxicity and mutagenesis readouts\",\n      \"pmids\": [\"19564618\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single lab\", \"Biochemical division of labor between zeta, kappa, and iota not reconstituted\"]\n    },\n    {\n      \"year\": 2012,\n      \"claim\": \"Showed POLH contributes to antibody diversification through pathways distinct from its replicative TLS role, broadening its physiological function.\",\n      \"evidence\": \"REV1AA Polh(-/-) and Ung(-/-)Polh(-/-) double-mutant mouse genetics with Ig gene hypermutation spectrum sequencing\",\n      \"pmids\": [\"22223762\", \"22960197\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Molecular basis of REV1–POLH cooperation for transversions undefined\", \"Single lab\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked POLH loss to a systemic phenotype, placing the polymerase upstream of p53-dependent cellular senescence in metabolic tissue.\",\n      \"evidence\": \"Pol eta knockout mice with metabolic phenotyping, DNA-damage/senescence markers, and pharmacological p53 inhibition rescue\",\n      \"pmids\": [\"26240351\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Tissue-specific lesion driving senescence not identified\", \"Single lab\"]\n    },\n    {\n      \"year\": 2019,\n      \"claim\": \"Identified post-transcriptional control of POLH expression as a determinant of chemoresistance.\",\n      \"evidence\": \"APA site mapping, 3'UTR reporter assays, miR-619 perturbation, and cisplatin sensitivity assays in cancer cell lines\",\n      \"pmids\": [\"31064846\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Upstream regulation of APA choice unknown\", \"Single lab\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Built a functional assay framework distinguishing pathogenic from benign POLH variants by coupling kinetics to cellular rescue.\",\n      \"evidence\": \"Recombinant kinetics on CTD templates plus CRISPR knockout complementation with UV/cisplatin sensitivity in 2023 and 2025 studies\",\n      \"pmids\": [\"36982269\", \"40334807\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Genotype–phenotype mapping to XP-V severity incomplete\", \"Protein-stability versus catalytic mechanisms not always separable\", \"Single lab\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Provided the first liganded POLH crystal structures, opening structure-guided inhibitor development against the polymerase.\",\n      \"evidence\": \"Fragment-based drug discovery with X-ray crystallography and in vitro biochemical inhibition assays\",\n      \"pmids\": [\"34900730\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Inhibitor specificity over other Y-family polymerases not established\", \"Cellular efficacy not demonstrated\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Raised a non-canonical transcriptional role for the POLH ortholog at retrotransposons, distinct from replicative lesion bypass.\",\n      \"evidence\": \"Drosophila genetic screen, CUT&Tag, mass spectrometry, proximity ligation, and RNA Pol II ChIP-seq\",\n      \"pmids\": [\"40966519\"],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"Findings in Drosophila, not replicated in mammalian systems\", \"Mechanistic link between PolH and RNA Pol II occupancy unresolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How pol eta is selectively recruited to and exchanged at sites of distinct lesion types, and whether its transcriptional/retrotransposon role exists in mammals, remain open.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Low\",\n      \"gaps\": [\"No mammalian validation of transcriptional role\", \"Lesion-specific polymerase switching mechanism uncharacterized in the corpus\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140097\", \"supporting_discovery_ids\": [0, 1, 8, 9]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [1]},\n      {\"term_id\": \"GO:0016740\", \"supporting_discovery_ids\": [1, 8]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-69306\", \"supporting_discovery_ids\": [0, 1]}\n    ],\n    \"complexes\": [],\n    \"partners\": [\"REV1\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}