{"gene":"POLR2F","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2001,"finding":"RPB6 is a sequence, structural, and functional homolog of bacterial RNAP omega subunit; both promote RNAP assembly via a 'latching' mechanism at the interface with the largest subunit (RPB1/beta'). Overproduction of RPB6 in yeast suppresses the assembly defect caused by substitution in RPB1 equivalent to the beta' residue suppressed by omega overproduction in E. coli. High-resolution structural analysis confirmed the RPB6-RPB1 interface is structurally homologous to the omega-beta' interface.","method":"Genetic suppression assay (overproduction rescue of assembly-defective mutants in yeast and E. coli), high-resolution structural analysis of omega-beta' interface compared with RPB6-RPB1 interface","journal":"Proceedings of the National Academy of Sciences of the United States of America","confidence":"High","confidence_rationale":"Tier 1 / Strong — structural analysis plus functional genetic suppression across two organisms with multiple orthogonal methods","pmids":["11158566"],"is_preprint":false},{"year":2000,"finding":"Rpb6 in fission yeast is a direct contact target of the transcription elongation factor TFIIS. Mutations in the essential C-terminal region (residues 61–139) of Rpb6 reduce RNAP II affinity for TFIIS, cause 6-azauracil sensitivity (transcription elongation defect), and both phenotypes are suppressed by TFIIS overexpression. Direct Rpb6–TFIIS interaction was demonstrated by GST-TFIIS pull-down of RNAP II, and excess Rpb6 competed with RNAP II for TFIIS binding.","method":"Genetic suppression (6-AU sensitivity, ts rescue by TFIIS overexpression), GST pull-down assay, competition binding experiment","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — reciprocal pull-down plus genetic suppression plus competition assay, single lab but multiple orthogonal methods","pmids":["10648612"],"is_preprint":false},{"year":2003,"finding":"A Q100R mutation in Rpb6 (conserved across eukaryotes and bacterial omega) causes selective loss of the Rpb4/Rpb7 subcomplex from RNAP II and III (but not RNAP I), significantly reducing their activities. Direct interaction experiments showed Rpb6 physically associates with Rpb4, indicating Rpb6 is a contact point for the Rpb4/Rpb7 subcomplex within RNAP II, revealing an assembly/stability role independent of its known RNAP assembly function.","method":"Conditional yeast mutant analysis, purification of mutant RNAP II, in vitro transcription activity assay, direct protein interaction experiments (pull-down/co-purification)","journal":"Molecular and cellular biology","confidence":"High","confidence_rationale":"Tier 2 / Moderate — purification of mutant complex, activity assay, and direct interaction experiments, single lab with multiple orthogonal approaches","pmids":["12697831"],"is_preprint":false},{"year":1994,"finding":"Fission yeast Rpb6 (142 aa) is essential for cell viability and encodes a phosphorylated subunit shared by all three nuclear RNA polymerases; the S. pombe gene fully complements complete deletion of the S. cerevisiae RPB6 homologue, demonstrating conserved essential function. The C-terminal half is identified as the most functionally critical region.","method":"Gene deletion complementation assay (heterospecific complementation), sequence analysis of genomic and cDNA copies","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — genetic complementation of deletion allele in a single study; limited mechanistic depth beyond essentiality","pmids":["8088549"],"is_preprint":false},{"year":1999,"finding":"Rat RPB6 is phosphorylated by casein kinase II (CKII) exclusively at serine-2 in the N-terminal acidic region in vitro. In-gel kinase assay of rat liver nuclear extract confirmed CKII as the predominant kinase phosphorylating RPB6 in the nucleus, implicating the N-terminal acidic region in phosphorylation-coupled regulatory functions.","method":"In vitro phosphorylation assay with recombinant CKII, site-directed mutagenesis of putative phosphorylation sites, RPB6-engaged in-gel kinase assay with nuclear extract","journal":"Gene","confidence":"Medium","confidence_rationale":"Tier 1 / Weak — in vitro kinase assay with mutagenesis confirming single phosphosite, single lab, no in vivo validation of site","pmids":["10393248"],"is_preprint":false},{"year":2014,"finding":"The C-terminal region of human RPAP2 (a Ser5-CTD phosphatase) directly interacts with the RNAP II subunit RPB6. RPAP2 occupies coding and 3' regions of protein-coding genes (MYC, GAPDH) by ChIP, and siRNA knockdown of RPAP2 causes defects in pre-mRNA 3'-end formation, indicating that RPB6 mediates RPAP2 recruitment/activity to control RNAP II activity and co-transcriptional 3'-end processing.","method":"Direct interaction assay (binding of RPAP2 C-terminal region to RPB6), chromatin immunoprecipitation (ChIP), siRNA knockdown with 3'-end formation analysis","journal":"Drug discoveries & therapeutics","confidence":"Medium","confidence_rationale":"Tier 2 / Weak — direct binding assay plus ChIP plus siRNA phenotype, single lab, moderate mechanistic depth","pmids":["25639305"],"is_preprint":false},{"year":2022,"finding":"The shared N-terminal tail (NTT) of RPB6 directly interacts with the PH domain (PH-D) of the p62 subunit of TFIIH, as determined by NMR structure of RPB6 free and bound to p62-PH-D. This interaction mediates recruitment of TFIIH to transcription sites and is a common mechanism for transcription-coupled nucleotide excision repair (TC-NER) by all three RNAPs (I, II, III). Point mutations in RPB6 NTT significantly reduce transcription from RNAPI-, RNAPII-, and RNAPIII-transcribed genes.","method":"NMR structure determination (RPB6 NTT free and bound to p62 PH-D), cryo-EM-based modeling of elongation complex, point mutagenesis of RPB6 NTT with transcription and TC-NER assays","journal":"Nucleic acids research","confidence":"High","confidence_rationale":"Tier 1 / Moderate — NMR structure with functional mutagenesis plus in vivo transcription and repair assays, single lab but multiple orthogonal methods","pmids":["34268577"],"is_preprint":false}],"current_model":"POLR2F (RPB6) is an essential shared subunit of all three nuclear RNA polymerases (I, II, III) that promotes RNAP assembly by 'latching' onto the largest subunit (RPB1) via a conserved mechanism homologous to bacterial omega subunit; its N-terminal tail directly contacts the p62 subunit of TFIIH to mediate transcription and transcription-coupled nucleotide excision repair across all three polymerase classes; its C-terminal core serves as a docking site for both the elongation factor TFIIS and the Rpb4/Rpb7 dissociable subcomplex; and its N-terminal acidic region is phosphorylated by casein kinase II at serine-2, suggesting a regulatory function. Additionally, RPAP2 directly binds RPB6 to participate in co-transcriptional pre-mRNA 3'-end formation."},"narrative":{"mechanistic_narrative":"POLR2F (RPB6) is an essential, phosphorylated subunit shared by all three nuclear RNA polymerases (I, II, III) that functions in polymerase assembly, stability, and the coordination of transcription with repair and RNA processing [PMID:8088549, PMID:11158566]. Mechanistically, RPB6 is the eukaryotic counterpart of the bacterial RNAP omega subunit: it 'latches' onto the largest subunit RPB1 to promote polymerase assembly, with the RPB6-RPB1 interface structurally homologous to the omega-beta' interface [PMID:11158566]. Its functionally critical C-terminal core serves as a docking platform for two distinct factors — the elongation factor TFIIS, whose binding is required to prevent transcription elongation defects [PMID:10648612], and the dissociable Rpb4/Rpb7 subcomplex, whose retention by RNAP II and III depends on a conserved RPB6 residue [PMID:12697831]. The shared N-terminal tail of RPB6 directly contacts the PH domain of the TFIIH p62 subunit, recruiting TFIIH to transcription sites as a common mechanism for transcription-coupled nucleotide excision repair across all three polymerase classes [PMID:34268577]. RPB6 additionally binds the C-terminal region of the CTD phosphatase RPAP2 to link the polymerase to co-transcriptional pre-mRNA 3'-end formation [PMID:25639305], and its N-terminal acidic region is phosphorylated by casein kinase II at serine-2 [PMID:10393248].","teleology":[{"year":1994,"claim":"Established that Rpb6 is an essential, conserved, phosphorylated subunit common to all three nuclear RNA polymerases and pinpointed its C-terminal half as the functionally critical region.","evidence":"Heterospecific gene deletion complementation between S. pombe and S. cerevisiae plus sequence analysis","pmids":["8088549"],"confidence":"Medium","gaps":["Did not define the molecular activity underlying essentiality","No structural basis for the C-terminal region's importance"]},{"year":1999,"claim":"Identified a regulatory post-translational modification by showing RPB6 is phosphorylated by casein kinase II at a single serine in its N-terminal acidic region.","evidence":"In vitro CKII phosphorylation with site-directed mutagenesis and in-gel kinase assay of rat liver nuclear extract","pmids":["10393248"],"confidence":"Medium","gaps":["No in vivo validation of the Ser-2 phosphosite","Functional consequence of phosphorylation not established"]},{"year":2000,"claim":"Defined the C-terminal region of Rpb6 as a direct docking site for the elongation factor TFIIS, linking the subunit to transcription elongation.","evidence":"GST-TFIIS pull-down of RNAP II, competition binding, and genetic suppression of 6-AU sensitivity by TFIIS overexpression in fission yeast","pmids":["10648612"],"confidence":"High","gaps":["Structural detail of the Rpb6-TFIIS interface not resolved","Did not address polymerase classes other than RNAP II"]},{"year":2001,"claim":"Resolved the molecular basis of RPB6 function by establishing it as the structural and functional homolog of the bacterial omega subunit that promotes polymerase assembly via a latching mechanism at RPB1.","evidence":"Cross-organism genetic suppression by overproduction of assembly-defective mutants and high-resolution structural comparison of the RPB6-RPB1 and omega-beta' interfaces","pmids":["11158566"],"confidence":"High","gaps":["Did not address whether the assembly role differs among RNAP I, II and III"]},{"year":2003,"claim":"Revealed an assembly/stability function distinct from latching, showing Rpb6 is a contact point that retains the Rpb4/Rpb7 subcomplex in RNAP II and III.","evidence":"Conditional Q100R yeast mutant, purification of mutant RNAP, in vitro transcription assays, and direct Rpb6-Rpb4 interaction experiments","pmids":["12697831"],"confidence":"High","gaps":["Why RNAP I is unaffected was not explained","Structural geometry of the Rpb6-Rpb4 contact not determined"]},{"year":2014,"claim":"Connected RPB6 to co-transcriptional RNA processing by showing it directly binds the CTD phosphatase RPAP2 to control RNAP II activity and pre-mRNA 3'-end formation.","evidence":"Direct binding of RPAP2 C-terminus to RPB6, ChIP at MYC/GAPDH, and siRNA knockdown with 3'-end formation analysis","pmids":["25639305"],"confidence":"Medium","gaps":["Single lab without reciprocal structural validation","Mechanism by which RPB6-RPAP2 binding controls 3'-end formation not detailed"]},{"year":2022,"claim":"Defined a shared molecular mechanism by which the RPB6 N-terminal tail recruits TFIIH via the p62 PH domain to drive transcription-coupled nucleotide excision repair across all three polymerases.","evidence":"NMR structure of RPB6 NTT free and bound to p62 PH-D, cryo-EM-based elongation complex modeling, and NTT point mutagenesis with transcription and TC-NER assays","pmids":["34268577"],"confidence":"High","gaps":["Whether NTT-p62 contact is regulated by CKII phosphorylation of the same N-terminal region not tested","Dynamics of TFIIH recruitment in vivo not resolved"]},{"year":null,"claim":"How RPB6's multiple binding functions (TFIIS, Rpb4/Rpb7, TFIIH-p62, RPAP2) and its CKII phosphorylation are coordinated or regulated within a single subunit remains unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No integrated model linking phosphorylation to interaction switching","Temporal ordering of factor binding during the transcription cycle unknown"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,3]},{"term_id":"GO:0060090","term_label":"molecular adaptor activity","supporting_discovery_ids":[1,5,6]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[3,4]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,6]},{"term_id":"R-HSA-73894","term_label":"DNA Repair","supporting_discovery_ids":[6]},{"term_id":"R-HSA-8953854","term_label":"Metabolism of RNA","supporting_discovery_ids":[5]}],"complexes":["RNA polymerase II","RNA polymerase I","RNA polymerase III"],"partners":["RPB1","TFIIS","RPB4","RPB7","RPAP2","GTF2H1"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P61218","full_name":"DNA-directed RNA polymerases I, II, and III subunit RPABC2","aliases":["DNA-directed RNA polymerase II subunit F","DNA-directed RNA polymerases I, II, and III 14.4 kDa polypeptide","RPABC14.4","RPB14.4","RPB6 homolog","RPC15"],"length_aa":127,"mass_kda":14.5,"function":"DNA-dependent RNA polymerase catalyzes the transcription of DNA into RNA using the four ribonucleoside triphosphates as substrates. Common component of RNA polymerases I, II, and III which synthesize ribosomal RNA precursors, mRNA precursors and many functional non-coding RNAs, and small RNAs, such as 5S rRNA and tRNAs, respectively. Pol II is the central component of the basal RNA polymerase II transcription machinery. Pols are composed of mobile elements that move relative to each other. In Pol II, POLR2F/RPABC2 is part of the clamp element and together with parts of POLR2A/RPB1 and POLR2B/RPB2 forms a pocket to which the POLR2D/RPB4-POLR2G/RPB7 subcomplex binds","subcellular_location":"Nucleus; Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/P61218/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/POLR2F","classification":"Common Essential","n_dependent_lines":1205,"n_total_lines":1208,"dependency_fraction":0.9975165562913907},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000100142","cell_line_id":"CID000701","localizations":[{"compartment":"nuclear_punctae","grade":3},{"compartment":"nucleolus_fc_dfc","grade":3},{"compartment":"nucleoplasm","grade":3},{"compartment":"cytoplasmic","grade":1}],"interactors":[{"gene":"POLR1C","stoichiometry":10.0},{"gene":"POLR1D","stoichiometry":10.0},{"gene":"POLR2B","stoichiometry":10.0},{"gene":"POLR2E","stoichiometry":10.0},{"gene":"CRCP","stoichiometry":10.0},{"gene":"POLR3D","stoichiometry":10.0},{"gene":"POLR2I","stoichiometry":10.0},{"gene":"POLR3A","stoichiometry":10.0},{"gene":"CD3EAP","stoichiometry":10.0},{"gene":"POLR2C","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000701","total_profiled":1310},"omim":[{"mim_id":"609881","title":"RNA POLYMERASE II, SUBUNIT J2; POLR2J2","url":"https://www.omim.org/entry/609881"},{"mim_id":"604414","title":"POLYMERASE II, RNA, SUBUNIT F; POLR2F","url":"https://www.omim.org/entry/604414"}],"hpa":{"profiled":true,"resolved_as":"","reliability":"Supported","locations":[{"location":"Nucleoplasm","reliability":"Supported"},{"location":"Nucleoli fibrillar center","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POLR2F"},"hgnc":{"alias_symbol":["RPB6","HRBP14.4"],"prev_symbol":[]},"alphafold":{"accession":"P61218","domains":[{"cath_id":"3.90.940.10","chopping":"51-127","consensus_level":"medium","plddt":94.1573,"start":51,"end":127}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P61218","model_url":"https://alphafold.ebi.ac.uk/files/AF-P61218-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P61218-F1-predicted_aligned_error_v6.png","plddt_mean":78.44},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLR2F","jax_strain_url":"https://www.jax.org/strain/search?query=POLR2F"},"sequence":{"accession":"P61218","fasta_url":"https://rest.uniprot.org/uniprotkb/P61218.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P61218/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P61218"}},"corpus_meta":[{"pmid":"11158566","id":"PMC_11158566","title":"Bacterial RNA polymerase subunit omega and eukaryotic RNA polymerase subunit RPB6 are sequence, structural, and functional homologs and promote RNA polymerase assembly.","date":"2001","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/11158566","citation_count":169,"is_preprint":false},{"pmid":"8088549","id":"PMC_8088549","title":"The fission yeast Schizosaccharomyces pombe rpb6 gene encodes the common phosphorylated subunit of RNA polymerase and complements a mutation in the corresponding gene of Saccharomyces cerevisiae.","date":"1994","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/8088549","citation_count":32,"is_preprint":false},{"pmid":"10648612","id":"PMC_10648612","title":"The Rpb6 subunit of fission yeast RNA polymerase II is a contact target of the transcription elongation factor TFIIS.","date":"2000","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/10648612","citation_count":32,"is_preprint":false},{"pmid":"12697831","id":"PMC_12697831","title":"Loss of the Rpb4/Rpb7 subcomplex in a mutant form of the Rpb6 subunit shared by RNA polymerases I, II, and III.","date":"2003","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/12697831","citation_count":31,"is_preprint":false},{"pmid":"1570325","id":"PMC_1570325","title":"Genes encoding transcription factor IIIA and the RNA polymerase common subunit RPB6 are divergently transcribed in Saccharomyces cerevisiae.","date":"1992","source":"Proceedings of the National Academy of Sciences of the United States of America","url":"https://pubmed.ncbi.nlm.nih.gov/1570325","citation_count":27,"is_preprint":false},{"pmid":"25639305","id":"PMC_25639305","title":"Human RNA polymerase II-associated protein 2 (RPAP2) interacts directly with the RNA polymerase II subunit Rpb6 and participates in pre-mRNA 3'-end formation.","date":"2014","source":"Drug discoveries & therapeutics","url":"https://pubmed.ncbi.nlm.nih.gov/25639305","citation_count":17,"is_preprint":false},{"pmid":"34268577","id":"PMC_34268577","title":"Three human RNA polymerases interact with TFIIH via a common RPB6 subunit.","date":"2022","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/34268577","citation_count":15,"is_preprint":false},{"pmid":"10393248","id":"PMC_10393248","title":"A serine residue in the N-terminal acidic region of rat RPB6, one of the common subunits of RNA polymerases, is exclusively phosphorylated by casein kinase II in vitro.","date":"1999","source":"Gene","url":"https://pubmed.ncbi.nlm.nih.gov/10393248","citation_count":14,"is_preprint":false},{"pmid":"10902924","id":"PMC_10902924","title":"Isolation and characterisation of a chick cDNA encoding the RNA polymerase common subunit RPB6.","date":"2000","source":"DNA sequence : the journal of DNA sequencing and mapping","url":"https://pubmed.ncbi.nlm.nih.gov/10902924","citation_count":3,"is_preprint":false},{"pmid":null,"id":"bio_10.1101_2025.05.12.653476","title":"Reorganizing the RNA polymerase II complex for replication of an infectious noncoding RNA in vivo","date":"2025-05-12","source":"bioRxiv","url":"https://doi.org/10.1101/2025.05.12.653476","citation_count":0,"is_preprint":true}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":6636,"output_tokens":2192,"usd":0.026394,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9192,"output_tokens":2813,"usd":0.058142,"stage2_stop_reason":"end_turn"},"total_usd":0.084536,"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\": 2001,\n      \"finding\": \"RPB6 is a sequence, structural, and functional homolog of bacterial RNAP omega subunit; both promote RNAP assembly via a 'latching' mechanism at the interface with the largest subunit (RPB1/beta'). Overproduction of RPB6 in yeast suppresses the assembly defect caused by substitution in RPB1 equivalent to the beta' residue suppressed by omega overproduction in E. coli. High-resolution structural analysis confirmed the RPB6-RPB1 interface is structurally homologous to the omega-beta' interface.\",\n      \"method\": \"Genetic suppression assay (overproduction rescue of assembly-defective mutants in yeast and E. coli), high-resolution structural analysis of omega-beta' interface compared with RPB6-RPB1 interface\",\n      \"journal\": \"Proceedings of the National Academy of Sciences of the United States of America\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — structural analysis plus functional genetic suppression across two organisms with multiple orthogonal methods\",\n      \"pmids\": [\"11158566\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Rpb6 in fission yeast is a direct contact target of the transcription elongation factor TFIIS. Mutations in the essential C-terminal region (residues 61–139) of Rpb6 reduce RNAP II affinity for TFIIS, cause 6-azauracil sensitivity (transcription elongation defect), and both phenotypes are suppressed by TFIIS overexpression. Direct Rpb6–TFIIS interaction was demonstrated by GST-TFIIS pull-down of RNAP II, and excess Rpb6 competed with RNAP II for TFIIS binding.\",\n      \"method\": \"Genetic suppression (6-AU sensitivity, ts rescue by TFIIS overexpression), GST pull-down assay, competition binding experiment\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal pull-down plus genetic suppression plus competition assay, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"10648612\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2003,\n      \"finding\": \"A Q100R mutation in Rpb6 (conserved across eukaryotes and bacterial omega) causes selective loss of the Rpb4/Rpb7 subcomplex from RNAP II and III (but not RNAP I), significantly reducing their activities. Direct interaction experiments showed Rpb6 physically associates with Rpb4, indicating Rpb6 is a contact point for the Rpb4/Rpb7 subcomplex within RNAP II, revealing an assembly/stability role independent of its known RNAP assembly function.\",\n      \"method\": \"Conditional yeast mutant analysis, purification of mutant RNAP II, in vitro transcription activity assay, direct protein interaction experiments (pull-down/co-purification)\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — purification of mutant complex, activity assay, and direct interaction experiments, single lab with multiple orthogonal approaches\",\n      \"pmids\": [\"12697831\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1994,\n      \"finding\": \"Fission yeast Rpb6 (142 aa) is essential for cell viability and encodes a phosphorylated subunit shared by all three nuclear RNA polymerases; the S. pombe gene fully complements complete deletion of the S. cerevisiae RPB6 homologue, demonstrating conserved essential function. The C-terminal half is identified as the most functionally critical region.\",\n      \"method\": \"Gene deletion complementation assay (heterospecific complementation), sequence analysis of genomic and cDNA copies\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — genetic complementation of deletion allele in a single study; limited mechanistic depth beyond essentiality\",\n      \"pmids\": [\"8088549\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 1999,\n      \"finding\": \"Rat RPB6 is phosphorylated by casein kinase II (CKII) exclusively at serine-2 in the N-terminal acidic region in vitro. In-gel kinase assay of rat liver nuclear extract confirmed CKII as the predominant kinase phosphorylating RPB6 in the nucleus, implicating the N-terminal acidic region in phosphorylation-coupled regulatory functions.\",\n      \"method\": \"In vitro phosphorylation assay with recombinant CKII, site-directed mutagenesis of putative phosphorylation sites, RPB6-engaged in-gel kinase assay with nuclear extract\",\n      \"journal\": \"Gene\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Weak — in vitro kinase assay with mutagenesis confirming single phosphosite, single lab, no in vivo validation of site\",\n      \"pmids\": [\"10393248\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2014,\n      \"finding\": \"The C-terminal region of human RPAP2 (a Ser5-CTD phosphatase) directly interacts with the RNAP II subunit RPB6. RPAP2 occupies coding and 3' regions of protein-coding genes (MYC, GAPDH) by ChIP, and siRNA knockdown of RPAP2 causes defects in pre-mRNA 3'-end formation, indicating that RPB6 mediates RPAP2 recruitment/activity to control RNAP II activity and co-transcriptional 3'-end processing.\",\n      \"method\": \"Direct interaction assay (binding of RPAP2 C-terminal region to RPB6), chromatin immunoprecipitation (ChIP), siRNA knockdown with 3'-end formation analysis\",\n      \"journal\": \"Drug discoveries & therapeutics\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Weak — direct binding assay plus ChIP plus siRNA phenotype, single lab, moderate mechanistic depth\",\n      \"pmids\": [\"25639305\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2022,\n      \"finding\": \"The shared N-terminal tail (NTT) of RPB6 directly interacts with the PH domain (PH-D) of the p62 subunit of TFIIH, as determined by NMR structure of RPB6 free and bound to p62-PH-D. This interaction mediates recruitment of TFIIH to transcription sites and is a common mechanism for transcription-coupled nucleotide excision repair (TC-NER) by all three RNAPs (I, II, III). Point mutations in RPB6 NTT significantly reduce transcription from RNAPI-, RNAPII-, and RNAPIII-transcribed genes.\",\n      \"method\": \"NMR structure determination (RPB6 NTT free and bound to p62 PH-D), cryo-EM-based modeling of elongation complex, point mutagenesis of RPB6 NTT with transcription and TC-NER assays\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — NMR structure with functional mutagenesis plus in vivo transcription and repair assays, single lab but multiple orthogonal methods\",\n      \"pmids\": [\"34268577\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLR2F (RPB6) is an essential shared subunit of all three nuclear RNA polymerases (I, II, III) that promotes RNAP assembly by 'latching' onto the largest subunit (RPB1) via a conserved mechanism homologous to bacterial omega subunit; its N-terminal tail directly contacts the p62 subunit of TFIIH to mediate transcription and transcription-coupled nucleotide excision repair across all three polymerase classes; its C-terminal core serves as a docking site for both the elongation factor TFIIS and the Rpb4/Rpb7 dissociable subcomplex; and its N-terminal acidic region is phosphorylated by casein kinase II at serine-2, suggesting a regulatory function. Additionally, RPAP2 directly binds RPB6 to participate in co-transcriptional pre-mRNA 3'-end formation.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLR2F (RPB6) is an essential, phosphorylated subunit shared by all three nuclear RNA polymerases (I, II, III) that functions in polymerase assembly, stability, and the coordination of transcription with repair and RNA processing [#3, #0]. Mechanistically, RPB6 is the eukaryotic counterpart of the bacterial RNAP omega subunit: it 'latches' onto the largest subunit RPB1 to promote polymerase assembly, with the RPB6-RPB1 interface structurally homologous to the omega-beta' interface [#0]. Its functionally critical C-terminal core serves as a docking platform for two distinct factors — the elongation factor TFIIS, whose binding is required to prevent transcription elongation defects [#1], and the dissociable Rpb4/Rpb7 subcomplex, whose retention by RNAP II and III depends on a conserved RPB6 residue [#2]. The shared N-terminal tail of RPB6 directly contacts the PH domain of the TFIIH p62 subunit, recruiting TFIIH to transcription sites as a common mechanism for transcription-coupled nucleotide excision repair across all three polymerase classes [#6]. RPB6 additionally binds the C-terminal region of the CTD phosphatase RPAP2 to link the polymerase to co-transcriptional pre-mRNA 3'-end formation [#5], and its N-terminal acidic region is phosphorylated by casein kinase II at serine-2 [#4].\"\n  ,\n  \"teleology\": [\n    {\n      \"year\": 1994,\n      \"claim\": \"Established that Rpb6 is an essential, conserved, phosphorylated subunit common to all three nuclear RNA polymerases and pinpointed its C-terminal half as the functionally critical region.\",\n      \"evidence\": \"Heterospecific gene deletion complementation between S. pombe and S. cerevisiae plus sequence analysis\",\n      \"pmids\": [\"8088549\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not define the molecular activity underlying essentiality\", \"No structural basis for the C-terminal region's importance\"]\n    },\n    {\n      \"year\": 1999,\n      \"claim\": \"Identified a regulatory post-translational modification by showing RPB6 is phosphorylated by casein kinase II at a single serine in its N-terminal acidic region.\",\n      \"evidence\": \"In vitro CKII phosphorylation with site-directed mutagenesis and in-gel kinase assay of rat liver nuclear extract\",\n      \"pmids\": [\"10393248\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No in vivo validation of the Ser-2 phosphosite\", \"Functional consequence of phosphorylation not established\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined the C-terminal region of Rpb6 as a direct docking site for the elongation factor TFIIS, linking the subunit to transcription elongation.\",\n      \"evidence\": \"GST-TFIIS pull-down of RNAP II, competition binding, and genetic suppression of 6-AU sensitivity by TFIIS overexpression in fission yeast\",\n      \"pmids\": [\"10648612\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Structural detail of the Rpb6-TFIIS interface not resolved\", \"Did not address polymerase classes other than RNAP II\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Resolved the molecular basis of RPB6 function by establishing it as the structural and functional homolog of the bacterial omega subunit that promotes polymerase assembly via a latching mechanism at RPB1.\",\n      \"evidence\": \"Cross-organism genetic suppression by overproduction of assembly-defective mutants and high-resolution structural comparison of the RPB6-RPB1 and omega-beta' interfaces\",\n      \"pmids\": [\"11158566\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Did not address whether the assembly role differs among RNAP I, II and III\"]\n    },\n    {\n      \"year\": 2003,\n      \"claim\": \"Revealed an assembly/stability function distinct from latching, showing Rpb6 is a contact point that retains the Rpb4/Rpb7 subcomplex in RNAP II and III.\",\n      \"evidence\": \"Conditional Q100R yeast mutant, purification of mutant RNAP, in vitro transcription assays, and direct Rpb6-Rpb4 interaction experiments\",\n      \"pmids\": [\"12697831\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Why RNAP I is unaffected was not explained\", \"Structural geometry of the Rpb6-Rpb4 contact not determined\"]\n    },\n    {\n      \"year\": 2014,\n      \"claim\": \"Connected RPB6 to co-transcriptional RNA processing by showing it directly binds the CTD phosphatase RPAP2 to control RNAP II activity and pre-mRNA 3'-end formation.\",\n      \"evidence\": \"Direct binding of RPAP2 C-terminus to RPB6, ChIP at MYC/GAPDH, and siRNA knockdown with 3'-end formation analysis\",\n      \"pmids\": [\"25639305\"],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Single lab without reciprocal structural validation\", \"Mechanism by which RPB6-RPAP2 binding controls 3'-end formation not detailed\"]\n    },\n    {\n      \"year\": 2022,\n      \"claim\": \"Defined a shared molecular mechanism by which the RPB6 N-terminal tail recruits TFIIH via the p62 PH domain to drive transcription-coupled nucleotide excision repair across all three polymerases.\",\n      \"evidence\": \"NMR structure of RPB6 NTT free and bound to p62 PH-D, cryo-EM-based elongation complex modeling, and NTT point mutagenesis with transcription and TC-NER assays\",\n      \"pmids\": [\"34268577\"],\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"Whether NTT-p62 contact is regulated by CKII phosphorylation of the same N-terminal region not tested\", \"Dynamics of TFIIH recruitment in vivo not resolved\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How RPB6's multiple binding functions (TFIIS, Rpb4/Rpb7, TFIIH-p62, RPAP2) and its CKII phosphorylation are coordinated or regulated within a single subunit remains unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"\",\n      \"gaps\": [\"No integrated model linking phosphorylation to interaction switching\", \"Temporal ordering of factor binding during the transcription cycle unknown\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 3]},\n      {\"term_id\": \"GO:0060090\", \"supporting_discovery_ids\": [1, 5, 6]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [3, 4]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 6]},\n      {\"term_id\": \"R-HSA-73894\", \"supporting_discovery_ids\": [6]},\n      {\"term_id\": \"R-HSA-8953854\", \"supporting_discovery_ids\": [5]}\n    ],\n    \"complexes\": [\n      \"RNA polymerase II\",\n      \"RNA polymerase I\",\n      \"RNA polymerase III\"\n    ],\n    \"partners\": [\n      \"RPB1\",\n      \"TFIIS\",\n      \"RPB4\",\n      \"RPB7\",\n      \"RPAP2\",\n      \"GTF2H1\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":5,"faith_total":5,"faith_pct":100.0}}