{"gene":"POLR3D","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":1987,"finding":"The human BN51 (POLR3D) gene complements a temperature-sensitive G1-phase cell cycle arrest mutation in BHK cells (tsBN51), and encodes a 395-amino-acid polypeptide with periodic repetitive clusters of acidic and basic amino acids arranged in four hydrophilic domains.","method":"Genomic DNA transfection complementation assay; cDNA cloning and sequencing","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — direct complementation rescue of ts mutant, cDNA isolation, sequencing, replicated across multiple transfection rounds","pmids":["3683386"],"is_preprint":false},{"year":1989,"finding":"The tsBN51 (POLR3D) gene locus maps to human chromosome 8, proximal to the c-myc amplification unit at 8q21, as established by somatic cell hybrid panel segregation and chromosomal in situ hybridization.","method":"Rodent-human somatic cell hybrid panel; chromosomal in situ hybridization","journal":"Genomics","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — two orthogonal localization methods, single lab","pmids":["2714790"],"is_preprint":false},{"year":1995,"finding":"BN51 (POLR3D) is a Pol III-specific subunit: the protein co-purifies with RNA Pol III activity, Pol III activity can be specifically immunoprecipitated from HeLa nuclear extracts using anti-BN51 antibodies, and the immunopurified BN51 complex restores both nonspecific and promoter-specific Pol III transcription activity in vitro.","method":"Co-purification with Pol III activity; immunoprecipitation of Pol III activity from HeLa nuclear extracts; in vitro transcription reconstitution with immunopurified complex","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — biochemical co-purification, reciprocal immunoprecipitation, and in vitro reconstitution of transcription activity, multiple orthogonal methods","pmids":["7799973"],"is_preprint":false},{"year":1995,"finding":"Loss of BN51 (POLR3D) function in tsBN51 cells at the nonpermissive temperature impairs processing of the 32S precursor rRNA into mature 5.8S and 28S rRNA, linking Pol III transcription to a post-transcriptional step in Pol I transcript maturation, likely via depletion of Pol III transcripts required for ribosome assembly.","method":"Temperature-sensitive mutant analysis; Northern blot/rRNA processing assay in tsBN51 cells","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — genetic loss-of-function with defined molecular phenotype (rRNA processing defect), single lab","pmids":["7799973"],"is_preprint":false},{"year":2008,"finding":"miR-320 directs transcriptional gene silencing of POLR3D by recruiting Argonaute-1 (AGO1), Polycomb group component EZH2, and tri-methyl histone H3 lysine 27 (H3K27me3) to the POLR3D promoter in mammalian cells, representing a cis-regulatory epigenetic mechanism.","method":"Chromatin immunoprecipitation (ChIP) for AGO1, EZH2, H3K27me3 at POLR3D promoter; miR-320 transfection and reporter assays","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — ChIP for multiple epigenetic marks and RISC components at the promoter, single lab","pmids":["18852463"],"is_preprint":false},{"year":2021,"finding":"Cryo-EM structures of the 17-subunit human Pol IIIα complex in backtracked and post-translocation states show that RPC10's N-ribbon docks on the RPC4 (POLR3D)-RPC5 heterodimer, while its C-ribbon inserts into the funnel of Pol III in the backtracked state and is more flexible in the post-translocation state.","method":"Cryo-EM structure determination of human Pol IIIα complex","journal":"Cell research","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structures at two functional states, direct structural definition of RPC4-RPC5 heterodimer interactions and RPC10 docking","pmids":["33674783"],"is_preprint":false},{"year":2023,"finding":"Biallelic pathogenic variants in POLR3D (a missense p.P181S and a splice site variant) cause significantly decreased POLR3D RNA expression, reduced expression of other Pol III subunit genes, aberrant Pol III transcription (decreased 7SK RNA and several tRNA genes), and altered interaction of Pol III with the PAQosome chaperone complex despite normal assembly of Pol III subunits, indicating the missense variant disrupts complex maturation rather than subunit incorporation.","method":"Functional studies in patient fibroblasts: RT-qPCR for Pol III transcripts; affinity purification coupled to mass spectrometry (AP-MS) of the POLR3D p.P181S variant","journal":"Frontiers in neurology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — AP-MS plus tRNA/7SK transcription assays in patient cells, single lab, two orthogonal methods","pmids":["37915380"],"is_preprint":false}],"current_model":"POLR3D (BN51/RPC4) is a Pol III-specific subunit that forms part of the RPC4-RPC5 heterodimer within the 17-subunit human RNA Pol III complex; it is essential for Pol III transcriptional activity (tRNA, 5S rRNA, 7SK RNA), interacts with the PAQosome chaperone complex during Pol III assembly/maturation, and its promoter is subject to miR-320-directed epigenetic silencing via AGO1/EZH2/H3K27me3 recruitment."},"narrative":{"mechanistic_narrative":"POLR3D (BN51/RPC4) is a Pol III-specific subunit required for RNA polymerase III transcription of small structured RNAs including 7SK RNA and tRNAs, originally identified through complementation of a temperature-sensitive G1-phase cell cycle arrest in BHK cells [PMID:3683386, PMID:37915380]. The protein co-purifies with Pol III activity, and immunopurified POLR3D-containing complex reconstitutes both nonspecific and promoter-specific Pol III transcription in vitro, establishing it as an integral, activity-essential subunit of the polymerase [PMID:7799973]. Within the 17-subunit human Pol III complex, POLR3D (RPC4) forms a heterodimer with RPC5 that serves as the docking platform for the RPC10 N-ribbon, a contact resolved in cryo-EM structures of backtracked and post-translocation states [PMID:33674783]. Beyond its catalytic role, POLR3D participates in Pol III complex maturation through the PAQosome chaperone complex, and biallelic pathogenic variants in POLR3D—a missense p.P181S together with a splice variant—reduce Pol III subunit expression and 7SK/tRNA transcription and disrupt the Pol III–PAQosome interaction without preventing subunit incorporation, defining a human disease arising from defective complex maturation [PMID:37915380]. POLR3D expression is itself constrained by a cis-regulatory epigenetic circuit in which miR-320 recruits AGO1, EZH2, and H3K27me3 to the POLR3D promoter to direct transcriptional silencing [PMID:18852463]. Loss of POLR3D function additionally impairs processing of the 32S precursor rRNA into mature 5.8S and 28S species, coupling Pol III output to ribosome biogenesis [PMID:7799973].","teleology":[{"year":1987,"claim":"Established that POLR3D (BN51) is an essential gene whose loss causes G1 cell cycle arrest, providing the first functional handle on the gene before its molecular role was known.","evidence":"Genomic DNA transfection complementation of the tsBN51 mutant in BHK cells, with cDNA cloning and sequencing","pmids":["3683386"],"confidence":"High","gaps":["The complementation phenotype did not reveal the biochemical activity of the protein","Why loss arrests cells specifically in G1 was not mechanistically defined"]},{"year":1989,"claim":"Mapped the gene to a defined chromosomal locus, anchoring it physically near 8q21 but not yet linking it to a pathway.","evidence":"Rodent-human somatic cell hybrid panel segregation and chromosomal in situ hybridization","pmids":["2714790"],"confidence":"Medium","gaps":["Localization alone provided no functional or mechanistic information","Single-lab mapping"]},{"year":1995,"claim":"Resolved the long-standing question of POLR3D's molecular identity by showing it is a Pol III-specific subunit whose complex is sufficient to restore transcription, converting a cell-cycle gene into a defined transcription machine component.","evidence":"Co-purification with Pol III activity, reciprocal immunoprecipitation from HeLa nuclear extracts, and in vitro transcription reconstitution","pmids":["7799973"],"confidence":"High","gaps":["The precise subunit interactions within Pol III were not resolved","How the subunit contributes to promoter-specific initiation was not defined"]},{"year":1995,"claim":"Connected Pol III transcriptional output to ribosome biogenesis by showing POLR3D loss impairs maturation of Pol I-derived rRNA, indicating cross-talk between the polymerase systems.","evidence":"Temperature-sensitive mutant analysis with Northern blot rRNA processing assay in tsBN51 cells","pmids":["7799973"],"confidence":"Medium","gaps":["The link is indirect, attributed to depletion of Pol III transcripts needed for assembly","Specific Pol III RNAs mediating the processing defect were not identified"]},{"year":2008,"claim":"Revealed that POLR3D expression is itself regulated by an miRNA-directed epigenetic silencing pathway, identifying a layer of transcriptional control over a polymerase subunit.","evidence":"ChIP for AGO1, EZH2, and H3K27me3 at the POLR3D promoter with miR-320 transfection and reporter assays","pmids":["18852463"],"confidence":"Medium","gaps":["The physiological contexts triggering this silencing were not defined","Single-lab evidence for the AGO1/EZH2 recruitment model"]},{"year":2021,"claim":"Defined the structural position of POLR3D (RPC4) within the assembled polymerase, showing the RPC4-RPC5 heterodimer docks the RPC10 N-ribbon across catalytic states.","evidence":"Cryo-EM structures of the 17-subunit human Pol IIIα complex in backtracked and post-translocation states","pmids":["33674783"],"confidence":"High","gaps":["The functional consequence of RPC10 docking on transcription fidelity was inferred, not directly tested","Dynamics of the heterodimer during initiation were not captured"]},{"year":2023,"claim":"Linked POLR3D to human Mendelian disease and pinpointed complex maturation, rather than subunit incorporation, as the disrupted step.","evidence":"Patient-fibroblast RT-qPCR of Pol III transcripts and AP-MS of the POLR3D p.P181S variant","pmids":["37915380"],"confidence":"Medium","gaps":["The clinical phenotype and disease name are not specified in the finding","How the PAQosome interaction defect translates to reduced transcription was not mechanistically dissected","Single-lab patient study"]},{"year":null,"claim":"How POLR3D-dependent Pol III maturation via the PAQosome is coordinated with cell-cycle progression and the original G1 arrest phenotype remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["The mechanistic bridge between the 1987 G1 arrest and the modern Pol III maturation model is uncharacterized in the corpus","No structural model of the POLR3D-PAQosome interaction"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[2,5]},{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[2,5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[2,4]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[2,5]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[3]}],"complexes":["RNA Polymerase III","RPC4-RPC5 heterodimer","PAQosome"],"partners":["POLR3E","POLR3K","AGO1","EZH2"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P05423","full_name":"DNA-directed RNA polymerase III subunit RPC4","aliases":["DNA-directed RNA polymerase III subunit D","Protein BN51","RNA polymerase III 47 kDa subunit","RPC53 homolog"],"length_aa":398,"mass_kda":44.4,"function":"DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates (PubMed:12391170, PubMed:20413673, PubMed:33558764, PubMed:34675218, PubMed:35637192). Specific peripheric component of RNA polymerase III (Pol III) which synthesizes small non-coding RNAs including 5S rRNA, snRNAs, tRNAs and miRNAs from at least 500 distinct genomic loci. Assembles with POLR3E/RPC5 forming a subcomplex that binds the Pol III core. Enables recruitment of Pol III at transcription initiation site and drives transcription initiation from both type 2 and type 3 DNA promoters. Required for efficient transcription termination and reinitiation (By similarity) (PubMed:12391170, PubMed:20413673, PubMed:35637192). Pol III plays a key role in sensing and limiting infection by intracellular bacteria and DNA viruses. Acts as nuclear and cytosolic DNA sensor involved in innate immune response. Can sense non-self dsDNA that serves as template for transcription into dsRNA. The non-self RNA polymerase III transcripts, such as Epstein-Barr virus-encoded RNAs (EBERs) induce type I interferon and NF-kappa-B through the RIG-I pathway (PubMed:19609254, PubMed:19631370)","subcellular_location":"Nucleus","url":"https://www.uniprot.org/uniprotkb/P05423/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/POLR3D","classification":"Common Essential","n_dependent_lines":633,"n_total_lines":1208,"dependency_fraction":0.5240066225165563},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000168495","cell_line_id":"CID000712","localizations":[{"compartment":"nuclear_punctae","grade":3},{"compartment":"nucleoplasm","grade":3}],"interactors":[{"gene":"POLR1C","stoichiometry":10.0},{"gene":"POLR1D","stoichiometry":10.0},{"gene":"POLR2E","stoichiometry":10.0},{"gene":"POLR2F","stoichiometry":10.0},{"gene":"POLR2H","stoichiometry":10.0},{"gene":"POLR2K","stoichiometry":10.0},{"gene":"POLR3A","stoichiometry":10.0},{"gene":"POLR3B","stoichiometry":10.0},{"gene":"POLR3C","stoichiometry":10.0},{"gene":"POLR3H","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000712","total_profiled":1310},"omim":[{"mim_id":"617457","title":"POLYMERASE III, RNA, SUBUNIT G-LIKE; POLR3GL","url":"https://www.omim.org/entry/617457"},{"mim_id":"617456","title":"POLYMERASE III, RNA, SUBUNIT G; POLR3G","url":"https://www.omim.org/entry/617456"},{"mim_id":"187280","title":"POLYMERASE III, RNA, SUBUNIT D; POLR3D","url":"https://www.omim.org/entry/187280"}],"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/POLR3D"},"hgnc":{"alias_symbol":["TSBN51","RPC4","C53"],"prev_symbol":["BN51T"]},"alphafold":{"accession":"P05423","domains":[{"cath_id":"-","chopping":"249-268_322-398","consensus_level":"medium","plddt":87.6519,"start":249,"end":398}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P05423","model_url":"https://alphafold.ebi.ac.uk/files/AF-P05423-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P05423-F1-predicted_aligned_error_v6.png","plddt_mean":64.12},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLR3D","jax_strain_url":"https://www.jax.org/strain/search?query=POLR3D"},"sequence":{"accession":"P05423","fasta_url":"https://rest.uniprot.org/uniprotkb/P05423.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P05423/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P05423"}},"corpus_meta":[{"pmid":"18852463","id":"PMC_18852463","title":"MicroRNA-directed transcriptional gene silencing in mammalian cells.","date":"2008","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/18852463","citation_count":539,"is_preprint":false},{"pmid":"1448111","id":"PMC_1448111","title":"Testicular expression of PC4 in the rat: molecular diversity of a novel germ cell-specific Kex2/subtilisin-like proprotein convertase.","date":"1992","source":"Molecular endocrinology (Baltimore, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/1448111","citation_count":187,"is_preprint":false},{"pmid":"28592558","id":"PMC_28592558","title":"Duplication and Loss of Function of Genes Encoding RNA Polymerase III Subunit C4 Causes Hybrid Incompatibility in Rice.","date":"2017","source":"G3 (Bethesda, Md.)","url":"https://pubmed.ncbi.nlm.nih.gov/28592558","citation_count":46,"is_preprint":false},{"pmid":"30519245","id":"PMC_30519245","title":"Exosomes and miRNA-Loaded Biomimetic Nanovehicles, a Focus on Their Potentials Preventing Type-2 Diabetes Linked to Metabolic Syndrome.","date":"2018","source":"Frontiers in immunology","url":"https://pubmed.ncbi.nlm.nih.gov/30519245","citation_count":44,"is_preprint":false},{"pmid":"23527852","id":"PMC_23527852","title":"Identification of new apolipoprotein-CIII glycoforms with ultrahigh resolution MALDI-FTICR mass spectrometry of human sera.","date":"2013","source":"Journal of proteome research","url":"https://pubmed.ncbi.nlm.nih.gov/23527852","citation_count":42,"is_preprint":false},{"pmid":"3683386","id":"PMC_3683386","title":"Isolation of the human gene that complements a temperature-sensitive cell cycle mutation in BHK cells.","date":"1987","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/3683386","citation_count":36,"is_preprint":false},{"pmid":"17275824","id":"PMC_17275824","title":"Characterization of the RNA polymerase II and III complexes in Leishmania major.","date":"2006","source":"International journal for parasitology","url":"https://pubmed.ncbi.nlm.nih.gov/17275824","citation_count":31,"is_preprint":false},{"pmid":"33674783","id":"PMC_33674783","title":"Structure of human RNA polymerase III elongation complex.","date":"2021","source":"Cell research","url":"https://pubmed.ncbi.nlm.nih.gov/33674783","citation_count":30,"is_preprint":false},{"pmid":"18485734","id":"PMC_18485734","title":"Recombinant proprotein convertase 4 (PC4) from Leishmania tarentolae expression system: purification, biochemical study and inhibitor design.","date":"2008","source":"Protein expression and purification","url":"https://pubmed.ncbi.nlm.nih.gov/18485734","citation_count":19,"is_preprint":false},{"pmid":"8946791","id":"PMC_8946791","title":"Simultaneous determination of cross-reactive leukotrienes in biological matrices using on-line liquid chromatography immunochemical detection.","date":"1996","source":"Analytical chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/8946791","citation_count":17,"is_preprint":false},{"pmid":"2714790","id":"PMC_2714790","title":"Chromosomal localization of human genes required for G1 progression in mammalian cells.","date":"1989","source":"Genomics","url":"https://pubmed.ncbi.nlm.nih.gov/2714790","citation_count":14,"is_preprint":false},{"pmid":"37915380","id":"PMC_37915380","title":"Biallelic pathogenic variants in POLR3D alter tRNA transcription and cause a hypomyelinating leukodystrophy: A case report.","date":"2023","source":"Frontiers in neurology","url":"https://pubmed.ncbi.nlm.nih.gov/37915380","citation_count":13,"is_preprint":false},{"pmid":"32707296","id":"PMC_32707296","title":"Time-resolved RNA-seq provided a new understanding of intestinal immune response of European eel (Anguilla anguilla) following infection with Aeromonas hydrophila.","date":"2020","source":"Fish & shellfish immunology","url":"https://pubmed.ncbi.nlm.nih.gov/32707296","citation_count":12,"is_preprint":false},{"pmid":"31456698","id":"PMC_31456698","title":"Oral Delivery of miRNA With Lipidic Aminoglycoside Derivatives in the Breastfed Rat.","date":"2019","source":"Frontiers in physiology","url":"https://pubmed.ncbi.nlm.nih.gov/31456698","citation_count":10,"is_preprint":false},{"pmid":"38391955","id":"PMC_38391955","title":"A Proteomic Investigation to Discover Candidate Proteins Involved in Novel Mechanisms of 5-Fluorouracil Resistance in Colorectal Cancer.","date":"2024","source":"Cells","url":"https://pubmed.ncbi.nlm.nih.gov/38391955","citation_count":9,"is_preprint":false},{"pmid":"7799973","id":"PMC_7799973","title":"The BN51 protein is a polymerase (Pol)-specific subunit of RNA Pol III which reveals a link between Pol III transcription and pre-rRNA processing.","date":"1995","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/7799973","citation_count":9,"is_preprint":false},{"pmid":"35432489","id":"PMC_35432489","title":"The Role of Copy Number Variants in Gene Co-Expression Patterns for Luminal B Breast Tumors.","date":"2022","source":"Frontiers in genetics","url":"https://pubmed.ncbi.nlm.nih.gov/35432489","citation_count":8,"is_preprint":false},{"pmid":"37170561","id":"PMC_37170561","title":"In-Depth Characterization of mAb Charge Variants by On-Line Multidimensional Liquid Chromatography-Mass Spectrometry.","date":"2023","source":"Analytical chemistry","url":"https://pubmed.ncbi.nlm.nih.gov/37170561","citation_count":8,"is_preprint":false},{"pmid":"36613633","id":"PMC_36613633","title":"Oral Delivery of miR-320-3p with Lipidic Aminoglycoside Derivatives at Mid-Lactation Alters miR-320-3p Endogenous Levels in the Gut and Brain of Adult Rats According to Early or Regular Weaning.","date":"2022","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/36613633","citation_count":5,"is_preprint":false},{"pmid":"28978030","id":"PMC_28978030","title":"Genetic profile and biological implication of PIN2/TRF1-interacting telomerase inhibitor 1 (PinX1) in human cancers: an analysis using The Cancer Genome Atlas.","date":"2017","source":"Oncotarget","url":"https://pubmed.ncbi.nlm.nih.gov/28978030","citation_count":5,"is_preprint":false},{"pmid":"40684265","id":"PMC_40684265","title":"Comprehensive genotype-phenotype analysis in POLR3-related disorders.","date":"2025","source":"HGG advances","url":"https://pubmed.ncbi.nlm.nih.gov/40684265","citation_count":3,"is_preprint":false},{"pmid":"40168905","id":"PMC_40168905","title":"Construction and expression of multi-stage antigen fusion protein RPC4 vaccine for Mycobacterium tuberculosis and its immunogenicity analysis in combination with adjuvant DIMQ.","date":"2025","source":"Tuberculosis (Edinburgh, Scotland)","url":"https://pubmed.ncbi.nlm.nih.gov/40168905","citation_count":2,"is_preprint":false},{"pmid":"40004102","id":"PMC_40004102","title":"Meta-Analysis of QTL Mapping and GWAS Reveal Candidate Genes for Heat Tolerance in Small Yellow Croaker, Larimichthys polyactis.","date":"2025","source":"International journal of molecular sciences","url":"https://pubmed.ncbi.nlm.nih.gov/40004102","citation_count":2,"is_preprint":false},{"pmid":"41634725","id":"PMC_41634725","title":"Study of POLR3A variants in a family trio suggests mutation-specific pathogenetic mechanisms: insights from integrative OMIC approaches.","date":"2026","source":"Cell communication and signaling : CCS","url":"https://pubmed.ncbi.nlm.nih.gov/41634725","citation_count":0,"is_preprint":false},{"pmid":"40966956","id":"PMC_40966956","title":"DUSP21 expression is associated with obstructive sleep apnea in pediatric patients with obesity.","date":"2025","source":"Sleep medicine","url":"https://pubmed.ncbi.nlm.nih.gov/40966956","citation_count":0,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":15339,"output_tokens":1794,"usd":0.036464,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":8602,"output_tokens":2702,"usd":0.05528,"stage2_stop_reason":"end_turn"},"total_usd":0.091744,"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\": 1987,\n      \"finding\": \"The human BN51 (POLR3D) gene complements a temperature-sensitive G1-phase cell cycle arrest mutation in BHK cells (tsBN51), and encodes a 395-amino-acid polypeptide with periodic repetitive clusters of acidic and basic amino acids arranged in four hydrophilic domains.\",\n      \"method\": \"Genomic DNA transfection complementation assay; cDNA cloning and sequencing\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — direct complementation rescue of ts mutant, cDNA isolation, sequencing, replicated across multiple transfection rounds\",\n      \"pmids\": [\"3683386\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1989,\n      \"finding\": \"The tsBN51 (POLR3D) gene locus maps to human chromosome 8, proximal to the c-myc amplification unit at 8q21, as established by somatic cell hybrid panel segregation and chromosomal in situ hybridization.\",\n      \"method\": \"Rodent-human somatic cell hybrid panel; chromosomal in situ hybridization\",\n      \"journal\": \"Genomics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — two orthogonal localization methods, single lab\",\n      \"pmids\": [\"2714790\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"BN51 (POLR3D) is a Pol III-specific subunit: the protein co-purifies with RNA Pol III activity, Pol III activity can be specifically immunoprecipitated from HeLa nuclear extracts using anti-BN51 antibodies, and the immunopurified BN51 complex restores both nonspecific and promoter-specific Pol III transcription activity in vitro.\",\n      \"method\": \"Co-purification with Pol III activity; immunoprecipitation of Pol III activity from HeLa nuclear extracts; in vitro transcription reconstitution with immunopurified complex\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — biochemical co-purification, reciprocal immunoprecipitation, and in vitro reconstitution of transcription activity, multiple orthogonal methods\",\n      \"pmids\": [\"7799973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1995,\n      \"finding\": \"Loss of BN51 (POLR3D) function in tsBN51 cells at the nonpermissive temperature impairs processing of the 32S precursor rRNA into mature 5.8S and 28S rRNA, linking Pol III transcription to a post-transcriptional step in Pol I transcript maturation, likely via depletion of Pol III transcripts required for ribosome assembly.\",\n      \"method\": \"Temperature-sensitive mutant analysis; Northern blot/rRNA processing assay in tsBN51 cells\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — genetic loss-of-function with defined molecular phenotype (rRNA processing defect), single lab\",\n      \"pmids\": [\"7799973\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"miR-320 directs transcriptional gene silencing of POLR3D by recruiting Argonaute-1 (AGO1), Polycomb group component EZH2, and tri-methyl histone H3 lysine 27 (H3K27me3) to the POLR3D promoter in mammalian cells, representing a cis-regulatory epigenetic mechanism.\",\n      \"method\": \"Chromatin immunoprecipitation (ChIP) for AGO1, EZH2, H3K27me3 at POLR3D promoter; miR-320 transfection and reporter 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 — ChIP for multiple epigenetic marks and RISC components at the promoter, single lab\",\n      \"pmids\": [\"18852463\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2021,\n      \"finding\": \"Cryo-EM structures of the 17-subunit human Pol IIIα complex in backtracked and post-translocation states show that RPC10's N-ribbon docks on the RPC4 (POLR3D)-RPC5 heterodimer, while its C-ribbon inserts into the funnel of Pol III in the backtracked state and is more flexible in the post-translocation state.\",\n      \"method\": \"Cryo-EM structure determination of human Pol IIIα complex\",\n      \"journal\": \"Cell research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structures at two functional states, direct structural definition of RPC4-RPC5 heterodimer interactions and RPC10 docking\",\n      \"pmids\": [\"33674783\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2023,\n      \"finding\": \"Biallelic pathogenic variants in POLR3D (a missense p.P181S and a splice site variant) cause significantly decreased POLR3D RNA expression, reduced expression of other Pol III subunit genes, aberrant Pol III transcription (decreased 7SK RNA and several tRNA genes), and altered interaction of Pol III with the PAQosome chaperone complex despite normal assembly of Pol III subunits, indicating the missense variant disrupts complex maturation rather than subunit incorporation.\",\n      \"method\": \"Functional studies in patient fibroblasts: RT-qPCR for Pol III transcripts; affinity purification coupled to mass spectrometry (AP-MS) of the POLR3D p.P181S variant\",\n      \"journal\": \"Frontiers in neurology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — AP-MS plus tRNA/7SK transcription assays in patient cells, single lab, two orthogonal methods\",\n      \"pmids\": [\"37915380\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLR3D (BN51/RPC4) is a Pol III-specific subunit that forms part of the RPC4-RPC5 heterodimer within the 17-subunit human RNA Pol III complex; it is essential for Pol III transcriptional activity (tRNA, 5S rRNA, 7SK RNA), interacts with the PAQosome chaperone complex during Pol III assembly/maturation, and its promoter is subject to miR-320-directed epigenetic silencing via AGO1/EZH2/H3K27me3 recruitment.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLR3D (BN51/RPC4) is a Pol III-specific subunit required for RNA polymerase III transcription of small structured RNAs including 7SK RNA and tRNAs, originally identified through complementation of a temperature-sensitive G1-phase cell cycle arrest in BHK cells [#0, #6]. The protein co-purifies with Pol III activity, and immunopurified POLR3D-containing complex reconstitutes both nonspecific and promoter-specific Pol III transcription in vitro, establishing it as an integral, activity-essential subunit of the polymerase [#2]. Within the 17-subunit human Pol III complex, POLR3D (RPC4) forms a heterodimer with RPC5 that serves as the docking platform for the RPC10 N-ribbon, a contact resolved in cryo-EM structures of backtracked and post-translocation states [#5]. Beyond its catalytic role, POLR3D participates in Pol III complex maturation through the PAQosome chaperone complex, and biallelic pathogenic variants in POLR3D—a missense p.P181S together with a splice variant—reduce Pol III subunit expression and 7SK/tRNA transcription and disrupt the Pol III\\u2013PAQosome interaction without preventing subunit incorporation, defining a human disease arising from defective complex maturation [#6]. POLR3D expression is itself constrained by a cis-regulatory epigenetic circuit in which miR-320 recruits AGO1, EZH2, and H3K27me3 to the POLR3D promoter to direct transcriptional silencing [#4]. Loss of POLR3D function additionally impairs processing of the 32S precursor rRNA into mature 5.8S and 28S species, coupling Pol III output to ribosome biogenesis [#3].\",\n  \"teleology\": [\n    {\n      \"year\": 1987,\n      \"claim\": \"Established that POLR3D (BN51) is an essential gene whose loss causes G1 cell cycle arrest, providing the first functional handle on the gene before its molecular role was known.\",\n      \"evidence\": \"Genomic DNA transfection complementation of the tsBN51 mutant in BHK cells, with cDNA cloning and sequencing\",\n      \"pmids\": [\"3683386\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The complementation phenotype did not reveal the biochemical activity of the protein\", \"Why loss arrests cells specifically in G1 was not mechanistically defined\"]\n    },\n    {\n      \"year\": 1989,\n      \"claim\": \"Mapped the gene to a defined chromosomal locus, anchoring it physically near 8q21 but not yet linking it to a pathway.\",\n      \"evidence\": \"Rodent-human somatic cell hybrid panel segregation and chromosomal in situ hybridization\",\n      \"pmids\": [\"2714790\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Localization alone provided no functional or mechanistic information\", \"Single-lab mapping\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Resolved the long-standing question of POLR3D's molecular identity by showing it is a Pol III-specific subunit whose complex is sufficient to restore transcription, converting a cell-cycle gene into a defined transcription machine component.\",\n      \"evidence\": \"Co-purification with Pol III activity, reciprocal immunoprecipitation from HeLa nuclear extracts, and in vitro transcription reconstitution\",\n      \"pmids\": [\"7799973\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The precise subunit interactions within Pol III were not resolved\", \"How the subunit contributes to promoter-specific initiation was not defined\"]\n    },\n    {\n      \"year\": 1995,\n      \"claim\": \"Connected Pol III transcriptional output to ribosome biogenesis by showing POLR3D loss impairs maturation of Pol I-derived rRNA, indicating cross-talk between the polymerase systems.\",\n      \"evidence\": \"Temperature-sensitive mutant analysis with Northern blot rRNA processing assay in tsBN51 cells\",\n      \"pmids\": [\"7799973\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The link is indirect, attributed to depletion of Pol III transcripts needed for assembly\", \"Specific Pol III RNAs mediating the processing defect were not identified\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Revealed that POLR3D expression is itself regulated by an miRNA-directed epigenetic silencing pathway, identifying a layer of transcriptional control over a polymerase subunit.\",\n      \"evidence\": \"ChIP for AGO1, EZH2, and H3K27me3 at the POLR3D promoter with miR-320 transfection and reporter assays\",\n      \"pmids\": [\"18852463\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The physiological contexts triggering this silencing were not defined\", \"Single-lab evidence for the AGO1/EZH2 recruitment model\"]\n    },\n    {\n      \"year\": 2021,\n      \"claim\": \"Defined the structural position of POLR3D (RPC4) within the assembled polymerase, showing the RPC4-RPC5 heterodimer docks the RPC10 N-ribbon across catalytic states.\",\n      \"evidence\": \"Cryo-EM structures of the 17-subunit human Pol III\\u03b1 complex in backtracked and post-translocation states\",\n      \"pmids\": [\"33674783\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"The functional consequence of RPC10 docking on transcription fidelity was inferred, not directly tested\", \"Dynamics of the heterodimer during initiation were not captured\"]\n    },\n    {\n      \"year\": 2023,\n      \"claim\": \"Linked POLR3D to human Mendelian disease and pinpointed complex maturation, rather than subunit incorporation, as the disrupted step.\",\n      \"evidence\": \"Patient-fibroblast RT-qPCR of Pol III transcripts and AP-MS of the POLR3D p.P181S variant\",\n      \"pmids\": [\"37915380\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The clinical phenotype and disease name are not specified in the finding\", \"How the PAQosome interaction defect translates to reduced transcription was not mechanistically dissected\", \"Single-lab patient study\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How POLR3D-dependent Pol III maturation via the PAQosome is coordinated with cell-cycle progression and the original G1 arrest phenotype remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"The mechanistic bridge between the 1987 G1 arrest and the modern Pol III maturation model is uncharacterized in the corpus\", \"No structural model of the POLR3D-PAQosome interaction\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [2, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [2, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [2, 5]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [3]}\n    ],\n    \"complexes\": [\n      \"RNA Polymerase III\",\n      \"RPC4-RPC5 heterodimer\",\n      \"PAQosome\"\n    ],\n    \"partners\": [\n      \"POLR3E\",\n      \"POLR3K\",\n      \"AGO1\",\n      \"EZH2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"tie","faith_supported":6,"faith_total":6,"faith_pct":100.0}}