{"gene":"POLR1A","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1988,"finding":"RPA190 (POLR1A ortholog in yeast) encodes the largest subunit (190 kDa) of RNA polymerase I; gene disruption experiments established it is essential for cell viability, and sequence analysis identified conserved homology regions (I–VI) shared with bacterial beta' and other eukaryotic polymerase large subunits, including a zinc-binding motif in the N-terminal region I implicated in DNA binding.","method":"Gene isolation, Southern hybridization, gene disruption, nuclease S1 mapping, amino acid sequence comparison","journal":"The Journal of biological chemistry","confidence":"High","confidence_rationale":"Tier 2 / Strong — gene disruption with viability readout plus detailed sequence/structural analysis replicated in multiple yeast polymerase studies","pmids":["2830265"],"is_preprint":false},{"year":1988,"finding":"Temperature-sensitive mutations in yeast RPA190 mapped to the conserved zinc-binding region I (rpa190-1 and rpa190-5) and between regions III–IV (rpa190-3) caused defective rRNA transcription in vivo and reduced RNA polymerase I activity in vitro, directly demonstrating the catalytic role of RPA190 in rDNA transcription.","method":"In vitro hydroxylamine mutagenesis, plasmid shuffle, pulse-label RNA analysis, partial purification and in vitro transcription assay, fine-structure mapping and sequencing of mutant alleles","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro transcription assay with defined mutants plus in vivo rRNA synthesis measurements; multiple mutant alleles mapped","pmids":["3054507"],"is_preprint":false},{"year":1990,"finding":"Conditional depletion of yeast RPA190 by replacement of its promoter with the galactose promoter revealed that reduced RNA polymerase I activity preferentially decreases rRNA synthesis, and that ribosomal protein accumulation subsequently declines to match the reduced rRNA level, largely through post-translational degradation of excess ribosomal proteins rather than translational regulation.","method":"Conditional promoter replacement (GAL1 promoter), pulse-chase labeling of proteins, polysome analysis, Northern blotting","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Strong — multiple orthogonal methods (metabolic labeling, polysome analysis, Northern blot) in a clean conditional depletion system","pmids":["2183018"],"is_preprint":false},{"year":2015,"finding":"Heterozygous mutations in human POLR1A (encoding the largest subunit of RNA polymerase I) cause acrofacial dysostosis by disrupting ribosome biogenesis, leading to p53-dependent apoptosis of neural-crest-derived skeletal precursor cells and consequent craniofacial anomalies, as demonstrated in polr1a mutant zebrafish.","method":"Zebrafish loss-of-function modeling (polr1a mutants), ribosome biogenesis assay, p53 pathway analysis, neural crest cell fate analysis","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 2 / Strong — in vivo zebrafish loss-of-function with mechanistic pathway placement (ribosome biogenesis → p53 → neural crest apoptosis → craniofacial defects)","pmids":["25913037"],"is_preprint":false},{"year":2017,"finding":"A homozygous missense variant in human POLR1A (p.Ser934Leu) causes leukodystrophy associated with decreased nucleolar RPA194 protein in patient fibroblasts, establishing that POLR1A loss-of-function in humans impairs RNA polymerase I function and leads to neurodegeneration.","method":"Exome sequencing, linkage analysis, immunofluorescence of patient skin fibroblasts (nucleolar RPA194 levels), segregation analysis","journal":"European journal of human genetics","confidence":"Medium","confidence_rationale":"Tier 3 / Moderate — patient fibroblast localization/protein level data plus genetic segregation; no in vitro reconstitution or enzymatic assay","pmids":["28051070"],"is_preprint":false},{"year":2023,"finding":"Pathogenic variants in POLR1A have variable effects on ribosomal RNA synthesis and nucleolar morphology in vitro; conditional knockout of Polr1a in neural crest cells, second heart field, or forebrain precursors in mice causes cell-autonomous apoptosis and embryonic malformations, establishing lineage-specific requirements for POLR1A-dependent ribosome biogenesis.","method":"In vitro rRNA synthesis assays, nucleolar morphology imaging, CRISPR-Cas9 knock-in of human variants in mice, conditional mutagenesis (Cre-lox) in defined developmental lineages","journal":"American journal of human genetics","confidence":"High","confidence_rationale":"Tier 1–2 / Strong — multiple orthogonal in vitro and in vivo methods, allelic series, conditional KO with defined cellular phenotypes across multiple lineages","pmids":["37075751"],"is_preprint":false},{"year":2023,"finding":"A homozygous POLR1A missense variant (p.Thr642Asn) causes aberrant pre-rRNA processing and degradation, abnormal nucleolar homeostasis, dysregulated protein homeostasis, and endoplasmic reticulum stress in patient fibroblasts, demonstrating that impaired RNA polymerase I activity propagates to ER stress and proteostasis failure.","method":"In vitro experiments in patient fibroblasts: rRNA processing assays, nucleolar morphology, proteomics, ER stress markers","journal":"Brain","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal methods (rRNA processing, proteomics, ER stress) in patient fibroblasts, single lab","pmids":["36917474"],"is_preprint":false},{"year":2025,"finding":"POLR1A promotes ferroptosis resistance by controlling TFAM expression via the transcription factor ATF4; the POLR1A–ATF4–TFAM axis suppresses mitophagy-dependent labile Fe²⁺ release, thereby limiting Fe²⁺-driven lipid peroxidation; POLR1A or TFAM inhibition increases Fe²⁺ accumulation and ferroptosis sensitivity, and CX-5461 (RNA Pol I inhibitor) synergizes with GPX4 blockade to induce ferroptotic death in vitro and in vivo.","method":"POLR1A knockdown/inhibition, TFAM expression analysis, mitophagy assays, labile iron measurement, lipid peroxidation assays, in vitro and in vivo combinatorial drug treatment (CX-5461 + GPX4 inhibitor)","journal":"Redox biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — multiple orthogonal mechanistic assays (iron, mitophagy, lipid peroxidation, in vivo) in a single lab; novel pathway not yet independently replicated","pmids":["40669210"],"is_preprint":false},{"year":2026,"finding":"Nuclear p85β (PIK3R2) undergoes liquid-liquid phase separation and accumulates in the fibrillar centers of nucleoli, where it physically interacts with and stabilizes POLR1A, enhancing rRNA biosynthesis in hepatocellular carcinoma cells.","method":"Co-immunoprecipitation, nucleolar fractionation, live-cell imaging of phase separation (LLPS), rRNA biosynthesis assays, knockdown/rescue experiments","journal":"International journal of biological sciences","confidence":"Medium","confidence_rationale":"Tier 2–3 / Moderate — Co-IP and functional rRNA assays from a single lab; LLPS and nucleolar localization experimentally demonstrated but no structural validation","pmids":["42212331"],"is_preprint":false}],"current_model":"POLR1A encodes the largest catalytic subunit of RNA polymerase I (Pol I), is essential for rDNA transcription and ribosome biogenesis, harbors a conserved zinc-binding domain required for activity, and its loss triggers p53-dependent apoptosis preferentially in neural-crest-derived cells; beyond its core transcriptional role, POLR1A also regulates ferroptosis resistance via an ATF4–TFAM axis controlling mitophagy and iron homeostasis, and is stabilized in nucleolar condensates by p85β to promote rRNA synthesis in cancer."},"narrative":{"mechanistic_narrative":"POLR1A encodes the largest catalytic subunit of RNA polymerase I, the enzyme dedicated to rDNA transcription and the production of pre-rRNA that drives ribosome biogenesis [PMID:2830265, PMID:3054507]. Work in yeast established that this subunit is essential for viability and carries conserved homology regions shared with other large polymerase subunits, including an N-terminal zinc-binding motif implicated in DNA binding; temperature-sensitive mutations mapping to this zinc region and to other conserved blocks abolish rRNA transcription in vivo and Pol I activity in vitro, directly placing POLR1A at the enzyme's catalytic core [PMID:2830265, PMID:3054507]. Reduced POLR1A activity preferentially diminishes rRNA synthesis, with excess ribosomal proteins subsequently cleared by post-translational degradation to match the lowered rRNA level [PMID:2183018]. In humans and vertebrate models, POLR1A mutations impair ribosome biogenesis and trigger p53-dependent apoptosis preferentially in neural-crest-derived skeletal precursors, causing acrofacial dysostosis, and conditional loss in defined developmental lineages produces cell-autonomous apoptosis and malformations [PMID:25913037, PMID:37075751]; other pathogenic variants reduce nucleolar Pol I protein, disrupt pre-rRNA processing and nucleolar homeostasis, and propagate to ER stress and proteostasis failure, manifesting as leukodystrophy and neurodegeneration [PMID:28051070, PMID:36917474]. Beyond canonical transcription, POLR1A is stabilized within nucleolar fibrillar centers by phase-separating nuclear p85β (PIK3R2) to enhance rRNA biosynthesis in hepatocellular carcinoma [PMID:42212331], and it promotes ferroptosis resistance through an ATF4–TFAM axis that suppresses mitophagy-dependent labile Fe²⁺ release, with Pol I inhibition synergizing with GPX4 blockade to induce ferroptotic death [PMID:40669210].","teleology":[{"year":1988,"claim":"Establishing what the largest Pol I subunit is and whether it is essential answered the foundational question of POLR1A's identity and necessity for cell life.","evidence":"Gene isolation and disruption with viability readout plus sequence comparison in yeast RPA190","pmids":["2830265"],"confidence":"High","gaps":["Catalytic contribution of the zinc-binding motif inferred from sequence homology, not yet functionally tested at this stage","Human ortholog function not addressed"]},{"year":1988,"claim":"Mapping temperature-sensitive mutations to conserved regions and showing defective transcription answered whether POLR1A is directly catalytic for rDNA transcription rather than merely structural.","evidence":"Mutagenesis, plasmid shuffle, in vivo pulse-label rRNA analysis, and in vitro transcription with defined yeast mutants","pmids":["3054507"],"confidence":"High","gaps":["Atomic-level catalytic mechanism not resolved","Did not establish how mutations alter enzyme assembly versus catalysis"]},{"year":1990,"claim":"Conditional depletion answered how lowered Pol I activity is buffered, showing rRNA synthesis is rate-limiting and excess ribosomal proteins are degraded post-translationally.","evidence":"GAL1 promoter replacement with pulse-chase labeling, polysome analysis, and Northern blotting in yeast","pmids":["2183018"],"confidence":"High","gaps":["Degradation machinery for excess ribosomal proteins not identified","Relevance to metazoan cells not established"]},{"year":2015,"claim":"Modeling human mutations in zebrafish answered why POLR1A defects cause tissue-specific disease, linking impaired ribosome biogenesis to p53-dependent neural crest apoptosis.","evidence":"Zebrafish polr1a loss-of-function with ribosome biogenesis, p53 pathway, and neural crest fate analysis","pmids":["25913037"],"confidence":"High","gaps":["Why neural crest is selectively vulnerable not mechanistically resolved","Direct demonstration in human tissue absent"]},{"year":2017,"claim":"Identifying a missense variant in a leukodystrophy patient extended the POLR1A disease spectrum and tied loss-of-function to reduced nucleolar Pol I protein and neurodegeneration.","evidence":"Exome sequencing, segregation analysis, and immunofluorescence of patient fibroblasts for nucleolar RPA194","pmids":["28051070"],"confidence":"Medium","gaps":["No in vitro reconstitution or enzymatic assay performed","Mechanism linking protein loss to neurodegeneration not defined"]},{"year":2023,"claim":"An allelic series with conditional mouse knockouts answered whether POLR1A requirements are lineage-specific and cell-autonomous across multiple developmental compartments.","evidence":"In vitro rRNA and nucleolar assays plus CRISPR knock-in mice and Cre-lox conditional mutagenesis in neural crest, second heart field, and forebrain","pmids":["37075751"],"confidence":"High","gaps":["Why different lineages show differing thresholds of sensitivity not resolved","Variant-specific severity not mapped to enzyme structure"]},{"year":2023,"claim":"Characterizing a processing-defective variant answered how impaired Pol I propagates downstream, linking aberrant pre-rRNA processing to nucleolar dysfunction, ER stress, and proteostasis failure.","evidence":"rRNA processing assays, proteomics, and ER stress markers in patient fibroblasts","pmids":["36917474"],"confidence":"Medium","gaps":["Single-lab, single patient genotype","Causal chain from rRNA defect to ER stress not dissected mechanistically"]},{"year":2025,"claim":"Connecting POLR1A to an ATF4–TFAM axis answered whether Pol I has a non-canonical role in cell death, identifying control of mitophagy-driven iron release and ferroptosis resistance.","evidence":"POLR1A knockdown/inhibition with TFAM analysis, mitophagy, labile iron and lipid peroxidation assays, and CX-5461 + GPX4 inhibitor combination in vitro and in vivo","pmids":["40669210"],"confidence":"Medium","gaps":["Novel pathway not independently replicated","How Pol I activity is mechanistically coupled to ATF4 not defined"]},{"year":2026,"claim":"Demonstrating p85β phase separation and POLR1A stabilization answered how Pol I output is regulated in cancer beyond intrinsic catalysis, via nucleolar condensate formation.","evidence":"Co-IP, nucleolar fractionation, LLPS live-cell imaging, and rRNA biosynthesis knockdown/rescue in hepatocellular carcinoma cells","pmids":["42212331"],"confidence":"Medium","gaps":["No structural validation of the interaction","Single-lab Co-IP without reciprocal in vivo confirmation"]},{"year":null,"claim":"How POLR1A integrates its core transcriptional role with its non-canonical regulation of iron homeostasis and condensate-mediated stabilization remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural model of human POLR1A within Pol I in the corpus","Mechanistic coupling between Pol I activity and the ATF4–TFAM ferroptosis axis undefined","Whether p85β condensate regulation operates outside cancer is unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[0,1,2]},{"term_id":"GO:0003677","term_label":"DNA binding","supporting_discovery_ids":[0]}],"localization":[{"term_id":"GO:0005730","term_label":"nucleolus","supporting_discovery_ids":[4,8]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,1,2]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[2,6]},{"term_id":"R-HSA-1266738","term_label":"Developmental Biology","supporting_discovery_ids":[3,5]},{"term_id":"R-HSA-5357801","term_label":"Programmed Cell Death","supporting_discovery_ids":[3,7]}],"complexes":["RNA polymerase I"],"partners":["PIK3R2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"O95602","full_name":"DNA-directed RNA polymerase I subunit RPA1","aliases":["A190","DNA-directed RNA polymerase I largest subunit","DNA-directed RNA polymerase I subunit A","RNA polymerase I 194 kDa subunit","RPA194"],"length_aa":1720,"mass_kda":194.8,"function":"Catalytic core component of RNA polymerase I (Pol I), a DNA-dependent RNA polymerase which synthesizes ribosomal RNA precursors using the four ribonucleoside triphosphates as substrates. Transcribes 47S pre-rRNAs from multicopy rRNA gene clusters, giving rise to 5.8S, 18S and 28S ribosomal RNAs (PubMed:11250903, PubMed:11283244, PubMed:16858408, PubMed:34671025, PubMed:34887565, PubMed:36271492). Pol I-mediated transcription cycle proceeds through transcription initiation, transcription elongation and transcription termination stages. During transcription initiation, Pol I pre-initiation complex (PIC) is recruited by the selectivity factor 1 (SL1/TIF-IB) complex bound to the core promoter that precedes an rDNA repeat unit. The PIC assembly bends the promoter favoring the formation of the transcription bubble and promoter escape. Once the polymerase has escaped from the promoter it enters the elongation phase during which RNA is actively polymerized, based on complementarity with the template DNA strand. Highly processive, assembles in structures referred to as 'Miller trees' where many elongating Pol I complexes queue and transcribe the same rDNA coding regions. At terminator sequences downstream of the rDNA gene, PTRF interacts with Pol I and halts Pol I transcription leading to the release of the RNA transcript and polymerase from the DNA (PubMed:11250903, PubMed:11283244, PubMed:16858408, PubMed:34671025, PubMed:34887565, PubMed:36271492). Forms Pol I active center together with the second largest subunit POLR1B/RPA2. Appends one nucleotide at a time to the 3' end of the nascent RNA, with POLR1A/RPA1 contributing a Mg(2+)-coordinating DxDGD motif, and POLR1B/RPA2 participating in the coordination of a second Mg(2+) ion and providing lysine residues believed to facilitate Watson-Crick base pairing between the incoming nucleotide and the template base. Typically, Mg(2+) ions direct a 5' nucleoside triphosphate to form a phosphodiester bond with the 3' hydroxyl of the preceding nucleotide of the nascent RNA, with the elimination of pyrophosphate. Has proofreading activity: Pauses and backtracks to allow the cleavage of a missincorporated nucleotide via POLR1H/RPA12. High Pol I processivity is associated with decreased transcription fidelity (By similarity) (PubMed:11250903, PubMed:11283244, PubMed:16858408, PubMed:34671025, PubMed:34887565, PubMed:36271492)","subcellular_location":"Nucleus, nucleolus; Chromosome","url":"https://www.uniprot.org/uniprotkb/O95602/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/POLR1A","classification":"Common Essential","n_dependent_lines":1203,"n_total_lines":1208,"dependency_fraction":0.9958609271523179},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000068654","cell_line_id":"CID000840","localizations":[{"compartment":"nucleolus_fc_dfc","grade":3}],"interactors":[{"gene":"POLR1B","stoichiometry":10.0},{"gene":"POLR2H","stoichiometry":10.0},{"gene":"POLR2K","stoichiometry":10.0},{"gene":"POLR1C","stoichiometry":4.0},{"gene":"POLR2E","stoichiometry":4.0},{"gene":"POLR2F","stoichiometry":4.0},{"gene":"CAPZB","stoichiometry":0.2}],"url":"https://opencell.sf.czbiohub.org/target/CID000840","total_profiled":1310},"omim":[{"mim_id":"620675","title":"LEUKODYSTROPHY, HYPOMYELINATING, 27; HLD27","url":"https://www.omim.org/entry/620675"},{"mim_id":"620341","title":"WD REPEAT-CONTAINING PROTEIN 75; WDR75","url":"https://www.omim.org/entry/620341"},{"mim_id":"619729","title":"ACTIN-RELATED PROTEIN 6; ACTR6","url":"https://www.omim.org/entry/619729"},{"mim_id":"616462","title":"ACROFACIAL DYSOSTOSIS, CINCINNATI TYPE; AFDCIN","url":"https://www.omim.org/entry/616462"},{"mim_id":"616404","title":"POLYMERASE I, RNA, SUBUNIT A; POLR1A","url":"https://www.omim.org/entry/616404"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Enhanced","locations":[{"location":"Nucleoli fibrillar center","reliability":"Enhanced"},{"location":"Nucleoplasm","reliability":"Additional"},{"location":"Cytosol","reliability":"Additional"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POLR1A"},"hgnc":{"alias_symbol":["DKFZP586M0122","FLJ21915","RPO1-4","RPA1","RPA190"],"prev_symbol":[]},"alphafold":{"accession":"O95602","domains":[{"cath_id":"4.10.860.120","chopping":"17-87_304-349_376-422","consensus_level":"medium","plddt":86.1612,"start":17,"end":422},{"cath_id":"-","chopping":"92-208_262-296","consensus_level":"medium","plddt":81.1764,"start":92,"end":296},{"cath_id":"2.40.40.20","chopping":"437-617","consensus_level":"medium","plddt":90.8525,"start":437,"end":617},{"cath_id":"1.10.274.100","chopping":"634-716_733-796","consensus_level":"high","plddt":91.3027,"start":634,"end":796},{"cath_id":"1.10.132.30","chopping":"801-954","consensus_level":"high","plddt":87.4621,"start":801,"end":954},{"cath_id":"3.30.70.2850","chopping":"1289-1362_1497-1555","consensus_level":"medium","plddt":83.1515,"start":1289,"end":1555}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/O95602","model_url":"https://alphafold.ebi.ac.uk/files/AF-O95602-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-O95602-F1-predicted_aligned_error_v6.png","plddt_mean":80.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLR1A","jax_strain_url":"https://www.jax.org/strain/search?query=POLR1A"},"sequence":{"accession":"O95602","fasta_url":"https://rest.uniprot.org/uniprotkb/O95602.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/O95602/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/O95602"}},"corpus_meta":[{"pmid":"2830265","id":"PMC_2830265","title":"RPA190, the gene coding for the largest subunit of yeast RNA polymerase A.","date":"1988","source":"The Journal of biological chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/2830265","citation_count":101,"is_preprint":false},{"pmid":"25913037","id":"PMC_25913037","title":"Acrofacial Dysostosis, Cincinnati Type, a Mandibulofacial Dysostosis Syndrome with Limb Anomalies, Is Caused by POLR1A Dysfunction.","date":"2015","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/25913037","citation_count":66,"is_preprint":false},{"pmid":"3054507","id":"PMC_3054507","title":"Isolation and characterization of temperature-sensitive mutations in RPA190, the gene encoding the largest subunit of RNA polymerase I from Saccharomyces cerevisiae.","date":"1988","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/3054507","citation_count":45,"is_preprint":false},{"pmid":"2183018","id":"PMC_2183018","title":"Conditional expression of RPA190, the gene encoding the largest subunit of yeast RNA polymerase I: effects of decreased rRNA synthesis on ribosomal protein synthesis.","date":"1990","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/2183018","citation_count":39,"is_preprint":false},{"pmid":"26551315","id":"PMC_26551315","title":"Metalaxyl Resistance in Phytophthora infestans: Assessing Role of RPA190 Gene and Diversity Within Clonal Lineages.","date":"2015","source":"Phytopathology","url":"https://pubmed.ncbi.nlm.nih.gov/26551315","citation_count":31,"is_preprint":false},{"pmid":"28051070","id":"PMC_28051070","title":"Severe neurodegenerative disease in brothers with homozygous mutation in POLR1A.","date":"2017","source":"European journal of human genetics : EJHG","url":"https://pubmed.ncbi.nlm.nih.gov/28051070","citation_count":24,"is_preprint":false},{"pmid":"29457681","id":"PMC_29457681","title":"Analysis of RPA190 revealed multiple positively selected mutations associated with metalaxyl resistance in Phytophthora infestans.","date":"2018","source":"Pest management science","url":"https://pubmed.ncbi.nlm.nih.gov/29457681","citation_count":19,"is_preprint":false},{"pmid":"37075751","id":"PMC_37075751","title":"POLR1A variants underlie phenotypic heterogeneity in craniofacial, neural, and cardiac anomalies.","date":"2023","source":"American journal of human genetics","url":"https://pubmed.ncbi.nlm.nih.gov/37075751","citation_count":16,"is_preprint":false},{"pmid":"40669210","id":"PMC_40669210","title":"POLR1A inhibits ferroptosis by regulating TFAM-mediated mitophagy and iron homeostasis.","date":"2025","source":"Redox biology","url":"https://pubmed.ncbi.nlm.nih.gov/40669210","citation_count":6,"is_preprint":false},{"pmid":"32860897","id":"PMC_32860897","title":"The RPA190-pc gene participates in the regulation of metalaxyl sensitivity, pathogenicity and growth in Phytophthora capsici.","date":"2020","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/32860897","citation_count":6,"is_preprint":false},{"pmid":"36917474","id":"PMC_36917474","title":"A homozygous POLR1A variant causes leukodystrophy and affects protein homeostasis.","date":"2023","source":"Brain : a journal of neurology","url":"https://pubmed.ncbi.nlm.nih.gov/36917474","citation_count":5,"is_preprint":false},{"pmid":"42212331","id":"PMC_42212331","title":"Phase separation of p85β modulates hepatocellular carcinoma progression through POLR1A.","date":"2026","source":"International journal of biological sciences","url":"https://pubmed.ncbi.nlm.nih.gov/42212331","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":8255,"output_tokens":2395,"usd":0.030345,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9671,"output_tokens":3287,"usd":0.065265,"stage2_stop_reason":"end_turn"},"total_usd":0.09561,"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\": 1988,\n      \"finding\": \"RPA190 (POLR1A ortholog in yeast) encodes the largest subunit (190 kDa) of RNA polymerase I; gene disruption experiments established it is essential for cell viability, and sequence analysis identified conserved homology regions (I–VI) shared with bacterial beta' and other eukaryotic polymerase large subunits, including a zinc-binding motif in the N-terminal region I implicated in DNA binding.\",\n      \"method\": \"Gene isolation, Southern hybridization, gene disruption, nuclease S1 mapping, amino acid sequence comparison\",\n      \"journal\": \"The Journal of biological chemistry\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — gene disruption with viability readout plus detailed sequence/structural analysis replicated in multiple yeast polymerase studies\",\n      \"pmids\": [\"2830265\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1988,\n      \"finding\": \"Temperature-sensitive mutations in yeast RPA190 mapped to the conserved zinc-binding region I (rpa190-1 and rpa190-5) and between regions III–IV (rpa190-3) caused defective rRNA transcription in vivo and reduced RNA polymerase I activity in vitro, directly demonstrating the catalytic role of RPA190 in rDNA transcription.\",\n      \"method\": \"In vitro hydroxylamine mutagenesis, plasmid shuffle, pulse-label RNA analysis, partial purification and in vitro transcription assay, fine-structure mapping and sequencing of mutant alleles\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro transcription assay with defined mutants plus in vivo rRNA synthesis measurements; multiple mutant alleles mapped\",\n      \"pmids\": [\"3054507\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1990,\n      \"finding\": \"Conditional depletion of yeast RPA190 by replacement of its promoter with the galactose promoter revealed that reduced RNA polymerase I activity preferentially decreases rRNA synthesis, and that ribosomal protein accumulation subsequently declines to match the reduced rRNA level, largely through post-translational degradation of excess ribosomal proteins rather than translational regulation.\",\n      \"method\": \"Conditional promoter replacement (GAL1 promoter), pulse-chase labeling of proteins, polysome analysis, Northern blotting\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — multiple orthogonal methods (metabolic labeling, polysome analysis, Northern blot) in a clean conditional depletion system\",\n      \"pmids\": [\"2183018\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2015,\n      \"finding\": \"Heterozygous mutations in human POLR1A (encoding the largest subunit of RNA polymerase I) cause acrofacial dysostosis by disrupting ribosome biogenesis, leading to p53-dependent apoptosis of neural-crest-derived skeletal precursor cells and consequent craniofacial anomalies, as demonstrated in polr1a mutant zebrafish.\",\n      \"method\": \"Zebrafish loss-of-function modeling (polr1a mutants), ribosome biogenesis assay, p53 pathway analysis, neural crest cell fate analysis\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Strong — in vivo zebrafish loss-of-function with mechanistic pathway placement (ribosome biogenesis → p53 → neural crest apoptosis → craniofacial defects)\",\n      \"pmids\": [\"25913037\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2017,\n      \"finding\": \"A homozygous missense variant in human POLR1A (p.Ser934Leu) causes leukodystrophy associated with decreased nucleolar RPA194 protein in patient fibroblasts, establishing that POLR1A loss-of-function in humans impairs RNA polymerase I function and leads to neurodegeneration.\",\n      \"method\": \"Exome sequencing, linkage analysis, immunofluorescence of patient skin fibroblasts (nucleolar RPA194 levels), segregation analysis\",\n      \"journal\": \"European journal of human genetics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 3 / Moderate — patient fibroblast localization/protein level data plus genetic segregation; no in vitro reconstitution or enzymatic assay\",\n      \"pmids\": [\"28051070\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Pathogenic variants in POLR1A have variable effects on ribosomal RNA synthesis and nucleolar morphology in vitro; conditional knockout of Polr1a in neural crest cells, second heart field, or forebrain precursors in mice causes cell-autonomous apoptosis and embryonic malformations, establishing lineage-specific requirements for POLR1A-dependent ribosome biogenesis.\",\n      \"method\": \"In vitro rRNA synthesis assays, nucleolar morphology imaging, CRISPR-Cas9 knock-in of human variants in mice, conditional mutagenesis (Cre-lox) in defined developmental lineages\",\n      \"journal\": \"American journal of human genetics\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1–2 / Strong — multiple orthogonal in vitro and in vivo methods, allelic series, conditional KO with defined cellular phenotypes across multiple lineages\",\n      \"pmids\": [\"37075751\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"A homozygous POLR1A missense variant (p.Thr642Asn) causes aberrant pre-rRNA processing and degradation, abnormal nucleolar homeostasis, dysregulated protein homeostasis, and endoplasmic reticulum stress in patient fibroblasts, demonstrating that impaired RNA polymerase I activity propagates to ER stress and proteostasis failure.\",\n      \"method\": \"In vitro experiments in patient fibroblasts: rRNA processing assays, nucleolar morphology, proteomics, ER stress markers\",\n      \"journal\": \"Brain\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal methods (rRNA processing, proteomics, ER stress) in patient fibroblasts, single lab\",\n      \"pmids\": [\"36917474\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2025,\n      \"finding\": \"POLR1A promotes ferroptosis resistance by controlling TFAM expression via the transcription factor ATF4; the POLR1A–ATF4–TFAM axis suppresses mitophagy-dependent labile Fe²⁺ release, thereby limiting Fe²⁺-driven lipid peroxidation; POLR1A or TFAM inhibition increases Fe²⁺ accumulation and ferroptosis sensitivity, and CX-5461 (RNA Pol I inhibitor) synergizes with GPX4 blockade to induce ferroptotic death in vitro and in vivo.\",\n      \"method\": \"POLR1A knockdown/inhibition, TFAM expression analysis, mitophagy assays, labile iron measurement, lipid peroxidation assays, in vitro and in vivo combinatorial drug treatment (CX-5461 + GPX4 inhibitor)\",\n      \"journal\": \"Redox biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — multiple orthogonal mechanistic assays (iron, mitophagy, lipid peroxidation, in vivo) in a single lab; novel pathway not yet independently replicated\",\n      \"pmids\": [\"40669210\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2026,\n      \"finding\": \"Nuclear p85β (PIK3R2) undergoes liquid-liquid phase separation and accumulates in the fibrillar centers of nucleoli, where it physically interacts with and stabilizes POLR1A, enhancing rRNA biosynthesis in hepatocellular carcinoma cells.\",\n      \"method\": \"Co-immunoprecipitation, nucleolar fractionation, live-cell imaging of phase separation (LLPS), rRNA biosynthesis assays, knockdown/rescue experiments\",\n      \"journal\": \"International journal of biological sciences\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2–3 / Moderate — Co-IP and functional rRNA assays from a single lab; LLPS and nucleolar localization experimentally demonstrated but no structural validation\",\n      \"pmids\": [\"42212331\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLR1A encodes the largest catalytic subunit of RNA polymerase I (Pol I), is essential for rDNA transcription and ribosome biogenesis, harbors a conserved zinc-binding domain required for activity, and its loss triggers p53-dependent apoptosis preferentially in neural-crest-derived cells; beyond its core transcriptional role, POLR1A also regulates ferroptosis resistance via an ATF4–TFAM axis controlling mitophagy and iron homeostasis, and is stabilized in nucleolar condensates by p85β to promote rRNA synthesis in cancer.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLR1A encodes the largest catalytic subunit of RNA polymerase I, the enzyme dedicated to rDNA transcription and the production of pre-rRNA that drives ribosome biogenesis [#0, #1]. Work in yeast established that this subunit is essential for viability and carries conserved homology regions shared with other large polymerase subunits, including an N-terminal zinc-binding motif implicated in DNA binding; temperature-sensitive mutations mapping to this zinc region and to other conserved blocks abolish rRNA transcription in vivo and Pol I activity in vitro, directly placing POLR1A at the enzyme's catalytic core [#0, #1]. Reduced POLR1A activity preferentially diminishes rRNA synthesis, with excess ribosomal proteins subsequently cleared by post-translational degradation to match the lowered rRNA level [#2]. In humans and vertebrate models, POLR1A mutations impair ribosome biogenesis and trigger p53-dependent apoptosis preferentially in neural-crest-derived skeletal precursors, causing acrofacial dysostosis, and conditional loss in defined developmental lineages produces cell-autonomous apoptosis and malformations [#3, #5]; other pathogenic variants reduce nucleolar Pol I protein, disrupt pre-rRNA processing and nucleolar homeostasis, and propagate to ER stress and proteostasis failure, manifesting as leukodystrophy and neurodegeneration [#4, #6]. Beyond canonical transcription, POLR1A is stabilized within nucleolar fibrillar centers by phase-separating nuclear p85\\u03b2 (PIK3R2) to enhance rRNA biosynthesis in hepatocellular carcinoma [#8], and it promotes ferroptosis resistance through an ATF4\\u2013TFAM axis that suppresses mitophagy-dependent labile Fe\\u00b2\\u207a release, with Pol I inhibition synergizing with GPX4 blockade to induce ferroptotic death [#7].\",\n  \"teleology\": [\n    {\n      \"year\": 1988,\n      \"claim\": \"Establishing what the largest Pol I subunit is and whether it is essential answered the foundational question of POLR1A's identity and necessity for cell life.\",\n      \"evidence\": \"Gene isolation and disruption with viability readout plus sequence comparison in yeast RPA190\",\n      \"pmids\": [\"2830265\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Catalytic contribution of the zinc-binding motif inferred from sequence homology, not yet functionally tested at this stage\", \"Human ortholog function not addressed\"]\n    },\n    {\n      \"year\": 1988,\n      \"claim\": \"Mapping temperature-sensitive mutations to conserved regions and showing defective transcription answered whether POLR1A is directly catalytic for rDNA transcription rather than merely structural.\",\n      \"evidence\": \"Mutagenesis, plasmid shuffle, in vivo pulse-label rRNA analysis, and in vitro transcription with defined yeast mutants\",\n      \"pmids\": [\"3054507\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Atomic-level catalytic mechanism not resolved\", \"Did not establish how mutations alter enzyme assembly versus catalysis\"]\n    },\n    {\n      \"year\": 1990,\n      \"claim\": \"Conditional depletion answered how lowered Pol I activity is buffered, showing rRNA synthesis is rate-limiting and excess ribosomal proteins are degraded post-translationally.\",\n      \"evidence\": \"GAL1 promoter replacement with pulse-chase labeling, polysome analysis, and Northern blotting in yeast\",\n      \"pmids\": [\"2183018\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Degradation machinery for excess ribosomal proteins not identified\", \"Relevance to metazoan cells not established\"]\n    },\n    {\n      \"year\": 2015,\n      \"claim\": \"Modeling human mutations in zebrafish answered why POLR1A defects cause tissue-specific disease, linking impaired ribosome biogenesis to p53-dependent neural crest apoptosis.\",\n      \"evidence\": \"Zebrafish polr1a loss-of-function with ribosome biogenesis, p53 pathway, and neural crest fate analysis\",\n      \"pmids\": [\"25913037\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why neural crest is selectively vulnerable not mechanistically resolved\", \"Direct demonstration in human tissue absent\"]\n    },\n    {\n      \"year\": 2017,\n      \"claim\": \"Identifying a missense variant in a leukodystrophy patient extended the POLR1A disease spectrum and tied loss-of-function to reduced nucleolar Pol I protein and neurodegeneration.\",\n      \"evidence\": \"Exome sequencing, segregation analysis, and immunofluorescence of patient fibroblasts for nucleolar RPA194\",\n      \"pmids\": [\"28051070\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No in vitro reconstitution or enzymatic assay performed\", \"Mechanism linking protein loss to neurodegeneration not defined\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"An allelic series with conditional mouse knockouts answered whether POLR1A requirements are lineage-specific and cell-autonomous across multiple developmental compartments.\",\n      \"evidence\": \"In vitro rRNA and nucleolar assays plus CRISPR knock-in mice and Cre-lox conditional mutagenesis in neural crest, second heart field, and forebrain\",\n      \"pmids\": [\"37075751\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Why different lineages show differing thresholds of sensitivity not resolved\", \"Variant-specific severity not mapped to enzyme structure\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Characterizing a processing-defective variant answered how impaired Pol I propagates downstream, linking aberrant pre-rRNA processing to nucleolar dysfunction, ER stress, and proteostasis failure.\",\n      \"evidence\": \"rRNA processing assays, proteomics, and ER stress markers in patient fibroblasts\",\n      \"pmids\": [\"36917474\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Single-lab, single patient genotype\", \"Causal chain from rRNA defect to ER stress not dissected mechanistically\"]\n    },\n    {\n      \"year\": 2025,\n      \"claim\": \"Connecting POLR1A to an ATF4\\u2013TFAM axis answered whether Pol I has a non-canonical role in cell death, identifying control of mitophagy-driven iron release and ferroptosis resistance.\",\n      \"evidence\": \"POLR1A knockdown/inhibition with TFAM analysis, mitophagy, labile iron and lipid peroxidation assays, and CX-5461 + GPX4 inhibitor combination in vitro and in vivo\",\n      \"pmids\": [\"40669210\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Novel pathway not independently replicated\", \"How Pol I activity is mechanistically coupled to ATF4 not defined\"]\n    },\n    {\n      \"year\": 2026,\n      \"claim\": \"Demonstrating p85\\u03b2 phase separation and POLR1A stabilization answered how Pol I output is regulated in cancer beyond intrinsic catalysis, via nucleolar condensate formation.\",\n      \"evidence\": \"Co-IP, nucleolar fractionation, LLPS live-cell imaging, and rRNA biosynthesis knockdown/rescue in hepatocellular carcinoma cells\",\n      \"pmids\": [\"42212331\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural validation of the interaction\", \"Single-lab Co-IP without reciprocal in vivo confirmation\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POLR1A integrates its core transcriptional role with its non-canonical regulation of iron homeostasis and condensate-mediated stabilization remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural model of human POLR1A within Pol I in the corpus\", \"Mechanistic coupling between Pol I activity and the ATF4\\u2013TFAM ferroptosis axis undefined\", \"Whether p85\\u03b2 condensate regulation operates outside cancer is unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"GO:0003677\", \"supporting_discovery_ids\": [0]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005730\", \"supporting_discovery_ids\": [4, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 1, 2]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [2, 6]},\n      {\"term_id\": \"R-HSA-1266738\", \"supporting_discovery_ids\": [3, 5]},\n      {\"term_id\": \"R-HSA-5357801\", \"supporting_discovery_ids\": [3, 7]}\n    ],\n    \"complexes\": [\"RNA polymerase I\"],\n    \"partners\": [\"PIK3R2\"],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}