{"gene":"POLK","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2000,"finding":"Human POLK-encoded DNA polymerase kappa (pol kappa) copies undamaged DNA with high error rates (average single-base substitution ~7×10⁻³ and deletion ~2×10⁻³), has unusual error specificity (high proportion of T·CMP mispairs and extraordinary rates of non-reiterated nucleotide deletions/additions), and possesses moderate processivity (chains of ≥25 nucleotides), with the C-terminal region (containing two zinc clusters) contributing to processivity. Pol kappa lacks detectable 3'→5' proofreading exonuclease activity.","method":"In vitro DNA polymerase fidelity assays, processivity assays, biochemical characterization of purified recombinant protein","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic assays with purified recombinant protein, multiple orthogonal measurements (substitution rate, deletion rate, processivity), replicated across labs","pmids":["11006276"],"is_preprint":false},{"year":2000,"finding":"Human POLK-encoded protein (named Pol theta by authors, now established as pol kappa) is a DNA polymerase that cannot bypass a cis-syn thymine-thymine dimer, a (6-4) photoproduct, or an abasic site. It misincorporates deoxynucleotides on non-damaged DNA templates with frequency ~10⁻³ to 10⁻⁴.","method":"Purification of hDINB1-encoded protein, in vitro DNA polymerase assay, steady-state kinetic analysis, lesion bypass assay","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct biochemical reconstitution with purified protein, multiple orthogonal assays (bypass assay, kinetic fidelity), consistent with independent reports","pmids":["10760255"],"is_preprint":false},{"year":2001,"finding":"Human pol kappa (POLK product) is a template-directed DNA polymerase that lacks detectable 3'→5' proofreading exonuclease activity, is not stimulated by PCNA in vitro, requires Mg²⁺ or Mn²⁺ as metal cofactor (Mg²⁺ preferred), is insensitive to aphidicolin and dideoxynucleotides, cannot bypass a cisplatin adduct, but shows limited bypass of a 2-acetylaminofluorene (AAF) lesion incorporating dCTP or dTTP (potentially mutagenic).","method":"GST-fusion protein expressed in insect cells, purified and tested in template-directed polymerase assay, lesion bypass assay, inhibitor sensitivity assays","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro enzymatic characterization with purified recombinant protein, multiple orthogonal assays","pmids":["11024016"],"is_preprint":false},{"year":2002,"finding":"Human POLK-encoded pol kappa is a promiscuous extender of primer-terminal mispairs on non-damaged DNA templates. It is also efficient at extending from a G opposite the 3'T of a cis-syn T-T dimer, implicating it in mutagenic bypass of T-T dimers via a two-polymerase mechanism. In its mismatch extension ability, pol kappa resembles pol zeta more than the phylogenetically related pol eta or pol iota.","method":"In vitro primer extension assay with purified pol kappa on templates with defined mismatches and lesions","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct in vitro biochemical assay with purified protein, multiple defined substrates tested","pmids":["11842189"],"is_preprint":false},{"year":1999,"finding":"Transient expression of mouse Dinb1 (POLK ortholog) cDNA in cultured mouse cells resulted in a ~10-fold increase in point mutations, with ~30% frameshift mutations, demonstrating that the POLK/Dinb1 product can promote mutagenesis in mammalian cells.","method":"Transient transfection of mammalian cells, mutation frequency assay","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — cellular gain-of-function with defined mutagenic phenotype, single lab, single method","pmids":["10620008"],"is_preprint":false},{"year":2004,"finding":"Wild-type p53, but not a DNA-binding-deficient mutant p53 (R273H), strongly inhibits POLK promoter activity in human lung cancer cell lines. POLK promoter activity is significantly higher in p53⁻/⁻ MEFs than in p53⁺/⁻ or p53⁺/⁺ MEFs, establishing p53 as a direct transcriptional repressor of POLK.","method":"Promoter-reporter assay, transcription start site mapping, comparison of p53⁻/⁻ vs p53⁺/⁺ MEFs","journal":"International journal of oncology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — promoter activity assay with mutagenesis control (R273H), genetic comparison across p53 genotypes, single lab","pmids":["15202001"],"is_preprint":false},{"year":2009,"finding":"Polk⁻/⁻ mice exhibit a spontaneous mutator phenotype with significantly increased mutation frequencies in kidney, liver, and lung (but not spleen or testis), with mutation spectra dominated by G:C base pair changes. This establishes Pol kappa as required for accurate translesion synthesis past naturally occurring DNA adducts in vivo.","method":"Polk knockout mouse model, lambda-phage cII reporter transgene mutation frequency assay across tissues","journal":"DNA repair","confidence":"High","confidence_rationale":"Tier 2 / Strong — clean KO mouse with defined in vivo mutagenic phenotype across multiple tissues using reporter transgene","pmids":["19783230"],"is_preprint":false},{"year":2009,"finding":"Introduction of a polymerase-dead point mutation into chicken POLK (in DT40 cells) phenocopies POLK knockout in sensitivity to methyl methanesulfonate (MMS), demonstrating that the catalytic polymerase activity of Pol kappa is required for repair of monoalkylation damage. The polymerase-dead Pol kappa does not interfere with other polymerases.","method":"Targeted knock-in of catalytic-dead mutation in chicken DT40 cells, MMS sensitivity assay, comparison with POLK⁻/⁻ double knockout","journal":"FEBS letters","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — active-site mutagenesis in cellular context with genetic epistasis, single lab","pmids":["19166845"],"is_preprint":false},{"year":2005,"finding":"Mouse Polkappa/human POLK gene produces multiple alternatively spliced transcripts specifically in testis (11 forms in mouse, 5 forms in human identified by RT-PCR), a phenomenon not shared by several other TLS polymerases, suggesting POLK may encode multiple Pol kappa isoforms in testis.","method":"RT-PCR amplification of coding sequence from testis cDNA","journal":"DNA repair","confidence":"Low","confidence_rationale":"Tier 3 / Weak — single detection method (RT-PCR), no functional validation of isoforms","pmids":["15661663"],"is_preprint":false},{"year":2015,"finding":"Somatic missense mutations in the catalytic core of POLK identified in prostate cancer (p.E29K, p.G154E, p.F155S, p.E430K, p.L442F) significantly diminish catalytic efficiency for lesion bypass (AP site) and increase misincorporation of T, C, and G compared to wild-type, functionally implicating these residues in TLS activity.","method":"Site-directed mutagenesis, bacterial expression and purification of POLK variants, in vitro TLS assay, nucleotide incorporation fidelity assay","journal":"Human mutation","confidence":"High","confidence_rationale":"Tier 1 / Moderate — site-directed mutagenesis combined with in vitro reconstitution and TLS assay; multiple mutants characterized biochemically","pmids":["26046662"],"is_preprint":false},{"year":2024,"finding":"POLK is highly expressed in mouse neurons. With chronological aging, there is a progressive reduction of nuclear POLK and concomitant accumulation in the cytoplasm. Nuclear POLK colocalizes with DNA damage sites and DNA repair proteins. Cytoplasmic POLK accumulates with stress granules and endo/lysosomal markers. Neuronal activity increases nuclear POLK levels and reduces the cytoplasmic fraction. Nuclear POLK is higher in GABAergic interneurons than excitatory pyramidal neurons.","method":"Immunofluorescence, longitudinal imaging, co-localization with DNA damage and repair markers, neuronal activity manipulation, subcellular fractionation-equivalent imaging in brain tissue","journal":"eLife","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — systematic longitudinal imaging with co-localization analysis and neuronal activity manipulation; single lab but multiple orthogonal approaches","pmids":["42126963","39026788"],"is_preprint":false},{"year":2024,"finding":"PTBP2 (an RNA-binding protein) stabilizes POLK mRNA via its 3'UTR, promoting increased Pol kappa protein production. PTBP2 knockout in CML cells increases DNA damage (comet assay, γH2AX foci), and overexpression of Pol kappa in PTBP2-KO cells restores normal phenotype. POLK interacts with MRE11 of the MRN complex, thereby governing ATM-CHK2 activation. Elevated PTBP2/Pol kappa promotes sister chromatid exchange and genomic instability.","method":"PTBP2 knockout CML cells, Pol kappa overexpression rescue, co-immunoprecipitation (POLK-MRE11 interaction), comet assay, γH2AX foci, SCE assay, BrdU incorporation","journal":"bioRxiv","confidence":"Low","confidence_rationale":"Tier 3 / Weak — preprint, single lab, Co-IP for interaction claim without reciprocal validation, multiple assays but not peer-reviewed","pmids":[],"is_preprint":true}],"current_model":"POLK encodes DNA polymerase kappa, a Y-family translesion synthesis (TLS) polymerase that replicates DNA with low fidelity and no proofreading activity, can extend mispaired primer termini and bypass certain bulky adducts (e.g., AAF) but not cisplatin adducts or TT dimers alone; its catalytic activity is required in vivo to suppress spontaneous mutagenesis (particularly at G:C sites) and to tolerate monoalkylation damage; its expression is transcriptionally repressed by p53; it is stabilized post-transcriptionally by PTBP2 and interacts with the MRN complex component MRE11; and in neurons its subcellular distribution shifts from nuclear to cytoplasmic with aging, with nuclear levels responsive to neuronal activity."},"narrative":{"mechanistic_narrative":"POLK encodes DNA polymerase kappa, a low-fidelity translesion synthesis (TLS) polymerase that replicates DNA across naturally occurring lesions and thereby suppresses spontaneous mutagenesis in vivo [PMID:11006276, PMID:19783230]. The enzyme copies even undamaged templates with high single-base substitution and deletion error rates, exhibits unusual error specificity favoring T·CMP mispairs and non-reiterated insertions/deletions, retains moderate processivity (a property contributed by its C-terminal zinc-cluster region), and lacks any 3'→5' proofreading exonuclease activity [PMID:11006276]. Its lesion-bypass capacity is selective: pol kappa cannot replicate past a cis-syn thymine-thymine dimer, a (6-4) photoproduct, an abasic site, or a cisplatin adduct, but it carries out limited, potentially mutagenic bypass of 2-acetylaminofluorene adducts and is a proficient extender of mispaired and lesion-associated primer termini, implicating it in a two-polymerase mode of mutagenic bypass [PMID:10760255, PMID:11024016, PMID:11842189]. Genetic ablation in mice produces a tissue-restricted spontaneous mutator phenotype dominated by G:C base-pair changes, and a catalytic-dead knock-in in chicken DT40 cells phenocopies the knockout for methyl methanesulfonate sensitivity, establishing that the catalytic activity itself is required for tolerance of monoalkylation damage [PMID:19783230, PMID:19166845]. POLK transcription is directly repressed by wild-type p53 acting through its promoter [PMID:15202001], and somatic catalytic-core missense mutations found in prostate cancer reduce bypass efficiency and elevate misincorporation, linking POLK function to genome stability in disease [PMID:26046662].","teleology":[{"year":2000,"claim":"Established the basic enzymatic identity of pol kappa as an error-prone, non-proofreading DNA polymerase, defining the fidelity and lesion-bypass constraints that frame its biological role.","evidence":"In vitro fidelity, processivity, and lesion-bypass assays with purified recombinant human protein","pmids":["11006276","10760255"],"confidence":"High","gaps":["Did not identify the physiological lesions it bypasses in cells","Structural basis of error specificity and zinc-cluster contribution to processivity not resolved"]},{"year":2001,"claim":"Refined the lesion-bypass specificity, showing pol kappa is blocked at cisplatin adducts but performs limited mutagenic bypass of AAF and is not stimulated by PCNA in vitro.","evidence":"Template-directed polymerase and lesion-bypass assays with purified GST-fusion protein, inhibitor sensitivity testing","pmids":["11024016"],"confidence":"High","gaps":["In vitro lack of PCNA stimulation does not establish cofactor requirements in cells","Range of bypassable adducts incompletely mapped"]},{"year":2002,"claim":"Identified pol kappa as a promiscuous mispair extender capable of extending past T-T dimer-associated mispairs, positioning it in a two-polymerase mutagenic bypass mechanism.","evidence":"In vitro primer extension on defined mismatch and lesion substrates with purified protein","pmids":["11842189"],"confidence":"High","gaps":["Partner inserter polymerase in cells not defined","Cellular context of two-polymerase bypass not demonstrated"]},{"year":2004,"claim":"Connected POLK to the DNA damage response by showing its promoter is directly repressed by wild-type p53, linking TLS capacity to tumor suppressor control.","evidence":"Promoter-reporter assays with DNA-binding-deficient p53 control and comparison across p53 genotype MEFs","pmids":["15202001"],"confidence":"Medium","gaps":["Direct p53 occupancy at the endogenous promoter not shown","Physiological consequence of derepression not measured"]},{"year":2009,"claim":"Demonstrated the in vivo requirement for pol kappa catalytic activity, showing knockout mice are spontaneous mutators (G:C-biased) and that catalytic-dead pol kappa phenocopies knockout for alkylation sensitivity.","evidence":"Polk knockout mouse with cII reporter mutation assay; catalytic-dead knock-in in DT40 cells with MMS sensitivity epistasis","pmids":["19783230","19166845"],"confidence":"High","gaps":["Specific endogenous adducts bypassed in each tissue not identified","Tissue restriction of the mutator phenotype mechanistically unexplained"]},{"year":2015,"claim":"Linked POLK catalytic function to human disease by showing cancer-associated catalytic-core mutations impair bypass and elevate misincorporation.","evidence":"Site-directed mutagenesis of prostate-cancer variants with in vitro TLS and fidelity assays","pmids":["26046662"],"confidence":"High","gaps":["Causal role of these variants in tumorigenesis not established","Cellular phenotype of the mutants not tested"]},{"year":2024,"claim":"Revealed regulation and localization dynamics of pol kappa: activity-dependent and age-dependent nuclear/cytoplasmic redistribution in neurons, and post-transcriptional stabilization by PTBP2 coupled to MRN/ATM-CHK2 signaling.","evidence":"Longitudinal immunofluorescence and co-localization in brain tissue; PTBP2-KO CML cells with rescue, Co-IP, comet, γH2AX, and SCE assays (PTBP2 study is a preprint)","pmids":["42126963","39026788"],"confidence":"Medium","gaps":["PTBP2-MRE11 axis rests on a single-lab preprint with Co-IP lacking reciprocal validation","Functional meaning of cytoplasmic pol kappa accumulation unknown","Mechanism coupling neuronal activity to nuclear pol kappa levels unresolved"]},{"year":null,"claim":"The physiological recruitment, regulation, and full repertoire of endogenous lesions handled by pol kappa in vivo remain incompletely defined.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of pol kappa engaging its native substrates in the timeline","Mechanism linking p53 repression and PTBP2 stabilization to cellular damage tolerance not integrated","Identity of inserter polymerases partnering pol kappa in cellular bypass unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140097","term_label":"catalytic activity, acting on DNA","supporting_discovery_ids":[0,1,2,3,9]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0,2]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[10]},{"term_id":"GO:0005829","term_label":"cytosol","supporting_discovery_ids":[10]}],"pathway":[{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[6,7,9]},{"term_id":"R-HSA-69306","term_label":"DNA Replication","supporting_discovery_ids":[0,1,2,3]}],"complexes":[],"partners":["MRE11","PTBP2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"Q9UBT6","full_name":"DNA polymerase kappa","aliases":["DINB protein","DINP"],"length_aa":870,"mass_kda":98.8,"function":"DNA polymerase specifically involved in DNA repair. Plays an important role in translesion synthesis, where the normal high-fidelity DNA polymerases cannot proceed and DNA synthesis stalls. Depending on the context, it inserts the correct base, but causes frequent base transitions, transversions and frameshifts. Lacks 3'-5' proofreading exonuclease activity. Forms a Schiff base with 5'-deoxyribose phosphate at abasic sites, but does not have lyase activity","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/Q9UBT6/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":false,"resolved_as":"","url":"https://depmap.org/portal/gene/POLK","classification":"Not Classified","n_dependent_lines":2,"n_total_lines":1208,"dependency_fraction":0.0016556291390728477},"opencell":{"profiled":false,"resolved_as":"","ensg_id":"","cell_line_id":"","localizations":[],"interactors":[{"gene":"RBM39","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/search/POLK","total_profiled":1310},"omim":[{"mim_id":"612472","title":"METHYLTRANSFERASE 3, N6-ADENOSINE-METHYLTRANSFERASE COMPLEX CATALYTIC SUBUNIT; METTL3","url":"https://www.omim.org/entry/612472"},{"mim_id":"606134","title":"REV1 DNA-DIRECTED POLYMERASE; REV1","url":"https://www.omim.org/entry/606134"},{"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"},{"mim_id":"605198","title":"TERMINAL NUCLEOTIDYLTRANSFERASE 4A; TENT4A","url":"https://www.omim.org/entry/605198"}],"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/POLK"},"hgnc":{"alias_symbol":["POLQ","DINP"],"prev_symbol":["DINB1"]},"alphafold":{"accession":"Q9UBT6","domains":[{"cath_id":"1.10.150.810","chopping":"1-73","consensus_level":"medium","plddt":79.951,"start":1,"end":73},{"cath_id":"1.10.150.810","chopping":"75-99_338-410","consensus_level":"medium","plddt":96.7726,"start":75,"end":410},{"cath_id":"3.30.70.270","chopping":"102-224_282-334","consensus_level":"medium","plddt":97.1471,"start":102,"end":334},{"cath_id":"3.30.1490.100","chopping":"414-520","consensus_level":"high","plddt":95.8408,"start":414,"end":520}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBT6","model_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBT6-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-Q9UBT6-F1-predicted_aligned_error_v6.png","plddt_mean":70.5},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLK","jax_strain_url":"https://www.jax.org/strain/search?query=POLK"},"sequence":{"accession":"Q9UBT6","fasta_url":"https://rest.uniprot.org/uniprotkb/Q9UBT6.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/Q9UBT6/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/Q9UBT6"}},"corpus_meta":[{"pmid":"9391106","id":"PMC_9391106","title":"Multiple 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Pol kappa lacks detectable 3'→5' proofreading exonuclease activity.\",\n      \"method\": \"In vitro DNA polymerase fidelity assays, processivity assays, biochemical characterization of purified recombinant protein\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic assays with purified recombinant protein, multiple orthogonal measurements (substitution rate, deletion rate, processivity), replicated across labs\",\n      \"pmids\": [\"11006276\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Human POLK-encoded protein (named Pol theta by authors, now established as pol kappa) is a DNA polymerase that cannot bypass a cis-syn thymine-thymine dimer, a (6-4) photoproduct, or an abasic site. It misincorporates deoxynucleotides on non-damaged DNA templates with frequency ~10⁻³ to 10⁻⁴.\",\n      \"method\": \"Purification of hDINB1-encoded protein, in vitro DNA polymerase assay, steady-state kinetic analysis, lesion bypass assay\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct biochemical reconstitution with purified protein, multiple orthogonal assays (bypass assay, kinetic fidelity), consistent with independent reports\",\n      \"pmids\": [\"10760255\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Human pol kappa (POLK product) is a template-directed DNA polymerase that lacks detectable 3'→5' proofreading exonuclease activity, is not stimulated by PCNA in vitro, requires Mg²⁺ or Mn²⁺ as metal cofactor (Mg²⁺ preferred), is insensitive to aphidicolin and dideoxynucleotides, cannot bypass a cisplatin adduct, but shows limited bypass of a 2-acetylaminofluorene (AAF) lesion incorporating dCTP or dTTP (potentially mutagenic).\",\n      \"method\": \"GST-fusion protein expressed in insect cells, purified and tested in template-directed polymerase assay, lesion bypass assay, inhibitor sensitivity assays\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro enzymatic characterization with purified recombinant protein, multiple orthogonal assays\",\n      \"pmids\": [\"11024016\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2002,\n      \"finding\": \"Human POLK-encoded pol kappa is a promiscuous extender of primer-terminal mispairs on non-damaged DNA templates. It is also efficient at extending from a G opposite the 3'T of a cis-syn T-T dimer, implicating it in mutagenic bypass of T-T dimers via a two-polymerase mechanism. In its mismatch extension ability, pol kappa resembles pol zeta more than the phylogenetically related pol eta or pol iota.\",\n      \"method\": \"In vitro primer extension assay with purified pol kappa on templates with defined mismatches and lesions\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct in vitro biochemical assay with purified protein, multiple defined substrates tested\",\n      \"pmids\": [\"11842189\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Transient expression of mouse Dinb1 (POLK ortholog) cDNA in cultured mouse cells resulted in a ~10-fold increase in point mutations, with ~30% frameshift mutations, demonstrating that the POLK/Dinb1 product can promote mutagenesis in mammalian cells.\",\n      \"method\": \"Transient transfection of mammalian cells, mutation frequency assay\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — cellular gain-of-function with defined mutagenic phenotype, single lab, single method\",\n      \"pmids\": [\"10620008\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2004,\n      \"finding\": \"Wild-type p53, but not a DNA-binding-deficient mutant p53 (R273H), strongly inhibits POLK promoter activity in human lung cancer cell lines. POLK promoter activity is significantly higher in p53⁻/⁻ MEFs than in p53⁺/⁻ or p53⁺/⁺ MEFs, establishing p53 as a direct transcriptional repressor of POLK.\",\n      \"method\": \"Promoter-reporter assay, transcription start site mapping, comparison of p53⁻/⁻ vs p53⁺/⁺ MEFs\",\n      \"journal\": \"International journal of oncology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — promoter activity assay with mutagenesis control (R273H), genetic comparison across p53 genotypes, single lab\",\n      \"pmids\": [\"15202001\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Polk⁻/⁻ mice exhibit a spontaneous mutator phenotype with significantly increased mutation frequencies in kidney, liver, and lung (but not spleen or testis), with mutation spectra dominated by G:C base pair changes. This establishes Pol kappa as required for accurate translesion synthesis past naturally occurring DNA adducts in vivo.\",\n      \"method\": \"Polk knockout mouse model, lambda-phage cII reporter transgene mutation frequency assay across tissues\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — clean KO mouse with defined in vivo mutagenic phenotype across multiple tissues using reporter transgene\",\n      \"pmids\": [\"19783230\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Introduction of a polymerase-dead point mutation into chicken POLK (in DT40 cells) phenocopies POLK knockout in sensitivity to methyl methanesulfonate (MMS), demonstrating that the catalytic polymerase activity of Pol kappa is required for repair of monoalkylation damage. The polymerase-dead Pol kappa does not interfere with other polymerases.\",\n      \"method\": \"Targeted knock-in of catalytic-dead mutation in chicken DT40 cells, MMS sensitivity assay, comparison with POLK⁻/⁻ double knockout\",\n      \"journal\": \"FEBS letters\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — active-site mutagenesis in cellular context with genetic epistasis, single lab\",\n      \"pmids\": [\"19166845\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"Mouse Polkappa/human POLK gene produces multiple alternatively spliced transcripts specifically in testis (11 forms in mouse, 5 forms in human identified by RT-PCR), a phenomenon not shared by several other TLS polymerases, suggesting POLK may encode multiple Pol kappa isoforms in testis.\",\n      \"method\": \"RT-PCR amplification of coding sequence from testis cDNA\",\n      \"journal\": \"DNA repair\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — single detection method (RT-PCR), no functional validation of isoforms\",\n      \"pmids\": [\"15661663\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Somatic missense mutations in the catalytic core of POLK identified in prostate cancer (p.E29K, p.G154E, p.F155S, p.E430K, p.L442F) significantly diminish catalytic efficiency for lesion bypass (AP site) and increase misincorporation of T, C, and G compared to wild-type, functionally implicating these residues in TLS activity.\",\n      \"method\": \"Site-directed mutagenesis, bacterial expression and purification of POLK variants, in vitro TLS assay, nucleotide incorporation fidelity assay\",\n      \"journal\": \"Human mutation\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — site-directed mutagenesis combined with in vitro reconstitution and TLS assay; multiple mutants characterized biochemically\",\n      \"pmids\": [\"26046662\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"POLK is highly expressed in mouse neurons. With chronological aging, there is a progressive reduction of nuclear POLK and concomitant accumulation in the cytoplasm. Nuclear POLK colocalizes with DNA damage sites and DNA repair proteins. Cytoplasmic POLK accumulates with stress granules and endo/lysosomal markers. Neuronal activity increases nuclear POLK levels and reduces the cytoplasmic fraction. Nuclear POLK is higher in GABAergic interneurons than excitatory pyramidal neurons.\",\n      \"method\": \"Immunofluorescence, longitudinal imaging, co-localization with DNA damage and repair markers, neuronal activity manipulation, subcellular fractionation-equivalent imaging in brain tissue\",\n      \"journal\": \"eLife\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — systematic longitudinal imaging with co-localization analysis and neuronal activity manipulation; single lab but multiple orthogonal approaches\",\n      \"pmids\": [\"42126963\", \"39026788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2024,\n      \"finding\": \"PTBP2 (an RNA-binding protein) stabilizes POLK mRNA via its 3'UTR, promoting increased Pol kappa protein production. PTBP2 knockout in CML cells increases DNA damage (comet assay, γH2AX foci), and overexpression of Pol kappa in PTBP2-KO cells restores normal phenotype. POLK interacts with MRE11 of the MRN complex, thereby governing ATM-CHK2 activation. Elevated PTBP2/Pol kappa promotes sister chromatid exchange and genomic instability.\",\n      \"method\": \"PTBP2 knockout CML cells, Pol kappa overexpression rescue, co-immunoprecipitation (POLK-MRE11 interaction), comet assay, γH2AX foci, SCE assay, BrdU incorporation\",\n      \"journal\": \"bioRxiv\",\n      \"confidence\": \"Low\",\n      \"confidence_rationale\": \"Tier 3 / Weak — preprint, single lab, Co-IP for interaction claim without reciprocal validation, multiple assays but not peer-reviewed\",\n      \"pmids\": [],\n      \"is_preprint\": true\n    }\n  ],\n  \"current_model\": \"POLK encodes DNA polymerase kappa, a Y-family translesion synthesis (TLS) polymerase that replicates DNA with low fidelity and no proofreading activity, can extend mispaired primer termini and bypass certain bulky adducts (e.g., AAF) but not cisplatin adducts or TT dimers alone; its catalytic activity is required in vivo to suppress spontaneous mutagenesis (particularly at G:C sites) and to tolerate monoalkylation damage; its expression is transcriptionally repressed by p53; it is stabilized post-transcriptionally by PTBP2 and interacts with the MRN complex component MRE11; and in neurons its subcellular distribution shifts from nuclear to cytoplasmic with aging, with nuclear levels responsive to neuronal activity.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLK encodes DNA polymerase kappa, a low-fidelity translesion synthesis (TLS) polymerase that replicates DNA across naturally occurring lesions and thereby suppresses spontaneous mutagenesis in vivo [#0, #6]. The enzyme copies even undamaged templates with high single-base substitution and deletion error rates, exhibits unusual error specificity favoring T\\u00b7CMP mispairs and non-reiterated insertions/deletions, retains moderate processivity (a property contributed by its C-terminal zinc-cluster region), and lacks any 3'\\u21925' proofreading exonuclease activity [#0]. Its lesion-bypass capacity is selective: pol kappa cannot replicate past a cis-syn thymine-thymine dimer, a (6-4) photoproduct, an abasic site, or a cisplatin adduct, but it carries out limited, potentially mutagenic bypass of 2-acetylaminofluorene adducts and is a proficient extender of mispaired and lesion-associated primer termini, implicating it in a two-polymerase mode of mutagenic bypass [#1, #2, #3]. Genetic ablation in mice produces a tissue-restricted spontaneous mutator phenotype dominated by G:C base-pair changes, and a catalytic-dead knock-in in chicken DT40 cells phenocopies the knockout for methyl methanesulfonate sensitivity, establishing that the catalytic activity itself is required for tolerance of monoalkylation damage [#6, #7]. POLK transcription is directly repressed by wild-type p53 acting through its promoter [#5], and somatic catalytic-core missense mutations found in prostate cancer reduce bypass efficiency and elevate misincorporation, linking POLK function to genome stability in disease [#9].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established the basic enzymatic identity of pol kappa as an error-prone, non-proofreading DNA polymerase, defining the fidelity and lesion-bypass constraints that frame its biological role.\",\n      \"evidence\": \"In vitro fidelity, processivity, and lesion-bypass assays with purified recombinant human protein\",\n      \"pmids\": [\n        \"11006276\",\n        \"10760255\"\n      ],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Did not identify the physiological lesions it bypasses in cells\",\n        \"Structural basis of error specificity and zinc-cluster contribution to processivity not resolved\"\n      ]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Refined the lesion-bypass specificity, showing pol kappa is blocked at cisplatin adducts but performs limited mutagenic bypass of AAF and is not stimulated by PCNA in vitro.\",\n      \"evidence\": \"Template-directed polymerase and lesion-bypass assays with purified GST-fusion protein, inhibitor sensitivity testing\",\n      \"pmids\": [\n        \"11024016\"\n      ],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"In vitro lack of PCNA stimulation does not establish cofactor requirements in cells\",\n        \"Range of bypassable adducts incompletely mapped\"\n      ]\n    },\n    {\n      \"year\": 2002,\n      \"claim\": \"Identified pol kappa as a promiscuous mispair extender capable of extending past T-T dimer-associated mispairs, positioning it in a two-polymerase mutagenic bypass mechanism.\",\n      \"evidence\": \"In vitro primer extension on defined mismatch and lesion substrates with purified protein\",\n      \"pmids\": [\n        \"11842189\"\n      ],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Partner inserter polymerase in cells not defined\",\n        \"Cellular context of two-polymerase bypass not demonstrated\"\n      ]\n    },\n    {\n      \"year\": 2004,\n      \"claim\": \"Connected POLK to the DNA damage response by showing its promoter is directly repressed by wild-type p53, linking TLS capacity to tumor suppressor control.\",\n      \"evidence\": \"Promoter-reporter assays with DNA-binding-deficient p53 control and comparison across p53 genotype MEFs\",\n      \"pmids\": [\n        \"15202001\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"Direct p53 occupancy at the endogenous promoter not shown\",\n        \"Physiological consequence of derepression not measured\"\n      ]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Demonstrated the in vivo requirement for pol kappa catalytic activity, showing knockout mice are spontaneous mutators (G:C-biased) and that catalytic-dead pol kappa phenocopies knockout for alkylation sensitivity.\",\n      \"evidence\": \"Polk knockout mouse with cII reporter mutation assay; catalytic-dead knock-in in DT40 cells with MMS sensitivity epistasis\",\n      \"pmids\": [\n        \"19783230\",\n        \"19166845\"\n      ],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Specific endogenous adducts bypassed in each tissue not identified\",\n        \"Tissue restriction of the mutator phenotype mechanistically unexplained\"\n      ]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Linked POLK catalytic function to human disease by showing cancer-associated catalytic-core mutations impair bypass and elevate misincorporation.\",\n      \"evidence\": \"Site-directed mutagenesis of prostate-cancer variants with in vitro TLS and fidelity assays\",\n      \"pmids\": [\n        \"26046662\"\n      ],\n      \"confidence\": \"High\",\n      \"gaps\": [\n        \"Causal role of these variants in tumorigenesis not established\",\n        \"Cellular phenotype of the mutants not tested\"\n      ]\n    },\n    {\n      \"year\": 2024,\n      \"claim\": \"Revealed regulation and localization dynamics of pol kappa: activity-dependent and age-dependent nuclear/cytoplasmic redistribution in neurons, and post-transcriptional stabilization by PTBP2 coupled to MRN/ATM-CHK2 signaling.\",\n      \"evidence\": \"Longitudinal immunofluorescence and co-localization in brain tissue; PTBP2-KO CML cells with rescue, Co-IP, comet, \\u03b3H2AX, and SCE assays (PTBP2 study is a preprint)\",\n      \"pmids\": [\n        \"42126963\",\n        \"39026788\"\n      ],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"PTBP2-MRE11 axis rests on a single-lab preprint with Co-IP lacking reciprocal validation\",\n        \"Functional meaning of cytoplasmic pol kappa accumulation unknown\",\n        \"Mechanism coupling neuronal activity to nuclear pol kappa levels unresolved\"\n      ]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"The physiological recruitment, regulation, and full repertoire of endogenous lesions handled by pol kappa in vivo remain incompletely defined.\",\n      \"evidence\": null,\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\n        \"No structural model of pol kappa engaging its native substrates in the timeline\",\n        \"Mechanism linking p53 repression and PTBP2 stabilization to cellular damage tolerance not integrated\",\n        \"Identity of inserter polymerases partnering pol kappa in cellular bypass unknown\"\n      ]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\n        \"term_id\": \"GO:0140097\",\n        \"supporting_discovery_ids\": [\n          0,\n          1,\n          2,\n          3,\n          9\n        ]\n      },\n      {\n        \"term_id\": \"GO:0003677\",\n        \"supporting_discovery_ids\": [\n          0,\n          2\n        ]\n      }\n    ],\n    \"localization\": [\n      {\n        \"term_id\": \"GO:0005634\",\n        \"supporting_discovery_ids\": [\n          10\n        ]\n      },\n      {\n        \"term_id\": \"GO:0005829\",\n        \"supporting_discovery_ids\": [\n          10\n        ]\n      }\n    ],\n    \"pathway\": [\n      {\n        \"term_id\": \"R-HSA-73894\",\n        \"supporting_discovery_ids\": [\n          6,\n          7,\n          9\n        ]\n      },\n      {\n        \"term_id\": \"R-HSA-69306\",\n        \"supporting_discovery_ids\": [\n          0,\n          1,\n          2,\n          3\n        ]\n      }\n    ],\n    \"complexes\": [],\n    \"partners\": [\n      \"MRE11\",\n      \"PTBP2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}