{"gene":"POLR2K","run_date":"2026-06-10T06:43:35","timeline":{"discoveries":[{"year":2020,"finding":"RTF1 Plus3 domain associates with Pol II subunit RPB12 (POLR2K) and the phosphorylated C-terminal region of DSIF subunit SPT5 within the complete Pol II elongation complex (EC*); RTF1 also forms four α-helices extending from the Plus3 domain along the Pol II protrusion and RPB10 to the polymerase funnel, and strongly stimulates Pol II elongation.","method":"Cryo-EM structure of complete porcine/human Pol II-DSIF-PAF-SPT6-RTF1 complex","journal":"Nature structural & molecular biology","confidence":"High","confidence_rationale":"Tier 1 / Strong — cryo-EM structure with functional validation (elongation stimulation assay), multiple orthogonal methods in a single rigorous study","pmids":["32541898"],"is_preprint":false},{"year":2018,"finding":"Gpn2 interacts directly with Rpb12 (POLR2K ortholog in yeast), and when Gpn2 is functionally defective the assembly of the Rpb3 subcomplex is disrupted, leading to defects in overall RNA polymerase II biogenesis.","method":"Co-immunoprecipitation, pulldown, and functional assembly assays in yeast","journal":"Molecular and cellular biology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reciprocal interaction demonstrated with defined assembly phenotype, single lab with two orthogonal methods","pmids":["29661922"],"is_preprint":false},{"year":2008,"finding":"Archaeal RNA polymerase subunit P (ortholog of eukaryotic Rpb12/POLR2K) is directly or indirectly required for stable open complex formation; the conserved zinc ribbon in the N-terminus is important for proper interaction with other RNA polymerase subunits, and the C-terminal 17-amino-acid peptide is sufficient to support basic RNA polymerase functions in vitro.","method":"In vitro transcription reconstitution assays with deletion mutants and cysteine substitutions in archaeal RNAP; complementation of yeast RPB12 deletion with archaeal subunit P","journal":"Molecular microbiology","confidence":"High","confidence_rationale":"Tier 1 / Strong — in vitro reconstitution with mutagenesis and complementation assays providing multiple orthogonal lines of evidence","pmids":["19183282"],"is_preprint":false},{"year":2009,"finding":"Archaeal subunit P (Rpb12/POLR2K ortholog) is not required for RNAP assembly per se but is essential for open complex formation; deletion of subunit P abolishes stable open complex formation while preserving the ability to extend a dinucleotide on a premelted template or RNA on an elongation scaffold.","method":"Reconstituted archaeal RNAP lacking subunit P tested in promoter-directed initiation, open complex formation, and elongation assays","journal":"Biochemical Society transactions","confidence":"Medium","confidence_rationale":"Tier 1 / Moderate — in vitro reconstitution with defined functional readouts, but single lab and largely consistent with PMID:19183282","pmids":["19143595"],"is_preprint":false},{"year":2000,"finding":"Archaeal RNA polymerase subunit P interacts with other archaeal subunits in a manner predicted from its eukaryotic Rpb12 counterpart; an archaeal-human F-RPB7 hybrid complex can form, demonstrating cross-kingdom functional conservation of the Rpb12 interaction interface.","method":"In vitro and in vivo protein interaction assays with recombinant subunits from Methanococcus jannaschii","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — in vitro and in vivo pulldown/interaction assays, single lab with two orthogonal approaches","pmids":["11058130"],"is_preprint":false},{"year":2006,"finding":"TbRPB12 (T. brucei ortholog of POLR2K) contains a conserved CX2CX10-15CX2C zinc-binding motif characteristic of eukaryotic RPB12 polypeptides and is a subunit of a transcriptionally active, alpha-amanitin-sensitive RNA polymerase II purified from T. brucei.","method":"Affinity purification of RNA Pol II and mass spectrometric identification; in vitro transcription activity assay with alpha-amanitin sensitivity test","journal":"Molecular and biochemical parasitology","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical purification with MS identification and functional transcription assay, single lab","pmids":["16962183"],"is_preprint":false},{"year":2005,"finding":"S. pombe TFIIEβ subunit binds Rpb12 (POLR2K ortholog) and Rpb2 subunits of Pol II, establishing a direct physical contact between TFIIE and Rpb12 at transcription initiation.","method":"In vitro binding/interaction assays between recombinant TFIIE subunits and individual Pol II subunits","journal":"Genes to cells : devoted to molecular & cellular mechanisms","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — direct binding assay showing specific interaction, single lab, single method","pmids":["15743411"],"is_preprint":false},{"year":2000,"finding":"Rpb12 (POLR2K ortholog) is assembled into the RNA polymerase II complex through multiple subunit-subunit contacts; co-expression experiments in insect cells established the assembly pathway involves Rpb3-mediated recruitment of subunits, with Rpb12 present in the assembled complex.","method":"Baculovirus co-expression of Pol II subunits in insect cells followed by sequential affinity chromatography (GST-Rpb3 and His-Rpb1) to isolate subunit complexes","journal":"Nucleic acids research","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — reconstitution in insect cells with affinity isolation, single lab","pmids":["10648788"],"is_preprint":false},{"year":2001,"finding":"Rpb12 (POLR2K ortholog) is one of the five subunits shared among RNA polymerases I, II and III in S. pombe; fractionation by glycerol gradient centrifugation showed that some excess Rpb12 exists in unassembled forms outside the Pol II holoenzyme.","method":"Quantitative immunoblotting and glycerol gradient centrifugation of whole-cell extracts","journal":"European journal of biochemistry","confidence":"Medium","confidence_rationale":"Tier 2 / Moderate — biochemical fractionation with quantitative analysis, single lab, two orthogonal methods","pmids":["11168400"],"is_preprint":false}],"current_model":"POLR2K (RPB12) is a small zinc ribbon-containing subunit shared among all three nuclear RNA polymerases that contributes to RNA Pol II complex integrity and elongation: its N-terminal zinc ribbon mediates proper interaction with other polymerase subunits, it is required (directly or indirectly) for stable promoter open complex formation, it serves as a docking site for the RTF1 Plus3 domain within the Pol II elongation complex to allosterically stimulate transcription, and its assembly into the Rpb3 subcomplex is facilitated by the biogenesis factor Gpn2."},"narrative":{"mechanistic_narrative":"POLR2K (RPB12) is a small zinc ribbon–containing subunit shared among the nuclear RNA polymerases that contributes to polymerase complex integrity, promoter open complex formation, and transcription elongation [PMID:19183282, PMID:11168400]. Its conserved N-terminal zinc ribbon (a CX2CX10-15CX2C motif) mediates proper interaction with other polymerase subunits, while a short C-terminal peptide is sufficient to support basic polymerase function in vitro [PMID:19183282, PMID:16962183]. The subunit is incorporated into the polymerase through Rpb3-mediated assembly of subunit subcomplexes, a process facilitated by the biogenesis factor Gpn2, whose loss disrupts Rpb3 subcomplex assembly and overall Pol II biogenesis [PMID:29661922, PMID:10648788]. At initiation, POLR2K makes direct physical contact with the TFIIEβ subunit and is required—directly or indirectly—for stable open complex formation [PMID:15743411, PMID:19183282, PMID:19143595]. During elongation it serves as a docking site for the RTF1 Plus3 domain within the complete Pol II elongation complex, where RTF1 strongly stimulates Pol II elongation [PMID:32541898]. Cross-kingdom complementation and hybrid-complex studies show the Rpb12 interaction interface is conserved from archaea to humans [PMID:19183282, PMID:11058130].","teleology":[{"year":2000,"claim":"Established that the Rpb12 interaction interface is functionally conserved across kingdoms and that the subunit engages defined polymerase partners as predicted from its eukaryotic counterpart.","evidence":"In vitro and in vivo interaction assays with recombinant Methanococcus jannaschii subunits, including an archaeal-human F-RPB7 hybrid complex","pmids":["11058130"],"confidence":"Medium","gaps":["Did not map the precise residues mediating the interface","No direct test in the human Pol II context"]},{"year":2000,"claim":"Defined how Rpb12 is incorporated into Pol II, showing it joins the complex through multiple subunit contacts during an Rpb3-mediated assembly pathway.","evidence":"Baculovirus co-expression of Pol II subunits in insect cells with sequential GST-Rpb3 and His-Rpb1 affinity chromatography","pmids":["10648788"],"confidence":"Medium","gaps":["Order of Rpb12 entry into the assembly pathway not resolved","No biogenesis factor identified at this stage"]},{"year":2001,"claim":"Showed Rpb12 is one of five subunits shared among Pol I, II and III and that a free, unassembled pool exists outside the holoenzyme.","evidence":"Quantitative immunoblotting and glycerol gradient centrifugation of S. pombe whole-cell extracts","pmids":["11168400"],"confidence":"Medium","gaps":["Function of the unassembled pool unknown","No regulatory role assigned to the shared distribution"]},{"year":2005,"claim":"Identified a direct initiation-stage contact, showing TFIIEβ binds Rpb12, linking the subunit to general transcription factor engagement.","evidence":"In vitro binding assays between recombinant S. pombe TFIIE subunits and individual Pol II subunits","pmids":["15743411"],"confidence":"Medium","gaps":["Interaction not validated in an intact preinitiation complex","Functional consequence of the TFIIEβ-Rpb12 contact not quantified"]},{"year":2006,"claim":"Confirmed Rpb12 is a bona fide subunit of an active eukaryotic Pol II in a divergent organism, with a conserved zinc-binding motif.","evidence":"Affinity purification of T. brucei Pol II with MS identification and alpha-amanitin-sensitive in vitro transcription assay","pmids":["16962183"],"confidence":"Medium","gaps":["No mutational dissection of the zinc motif in this system","Specific mechanistic role within the complex not addressed"]},{"year":2009,"claim":"Separated the subunit's roles in assembly versus catalysis, demonstrating it is dispensable for RNAP assembly but essential for stable open complex formation.","evidence":"Reconstituted archaeal RNAP lacking subunit P tested in initiation, open complex, and elongation assays","pmids":["19143595"],"confidence":"Medium","gaps":["Whether the open-complex requirement is direct or indirect not resolved","Largely overlapping with the same lab's complementary study"]},{"year":2008,"claim":"Pinpointed structural determinants of function, showing the N-terminal zinc ribbon is needed for subunit interactions while a 17-residue C-terminal peptide suffices for basic polymerase activity, with archaeal subunit P complementing yeast RPB12.","evidence":"In vitro transcription reconstitution with deletion/cysteine-substitution mutants and cross-kingdom yeast complementation","pmids":["19183282"],"confidence":"High","gaps":["Mechanism by which the subunit enables open complex formation not defined","Not extended to the human Pol II enzyme"]},{"year":2018,"claim":"Identified a dedicated biogenesis factor, showing Gpn2 binds Rpb12 and is required for Rpb3 subcomplex assembly and overall Pol II biogenesis.","evidence":"Co-immunoprecipitation, pulldown, and functional assembly assays in yeast","pmids":["29661922"],"confidence":"Medium","gaps":["Structural basis of the Gpn2-Rpb12 interaction unknown","Whether Gpn2 acts directly on Rpb12 or downstream of it not fully resolved"]},{"year":2020,"claim":"Defined a discrete elongation function, showing Rpb12 serves as a docking site for the RTF1 Plus3 domain in the complete Pol II elongation complex, coupling this contact to strong elongation stimulation.","evidence":"Cryo-EM of the complete porcine/human Pol II-DSIF-PAF-SPT6-RTF1 complex with elongation stimulation assay","pmids":["32541898"],"confidence":"High","gaps":["Quantitative contribution of the Rpb12 contact alone to RTF1 stimulation not isolated","Regulation of RTF1 docking in vivo not addressed"]},{"year":null,"claim":"How the human POLR2K zinc ribbon mechanistically enables open complex formation and how its assembly, initiation, and elongation roles are coordinated in vivo remain unresolved.","evidence":"","pmids":[],"confidence":"Medium","gaps":["No structural mechanism linking Rpb12 to open complex stability","No in vivo dissection of separable functions in human cells"]}],"mechanism_profile":{"molecular_activity":[{"term_id":"GO:0005198","term_label":"structural molecule activity","supporting_discovery_ids":[0,2,7]},{"term_id":"GO:0140098","term_label":"catalytic activity, acting on RNA","supporting_discovery_ids":[2,3,5]}],"localization":[{"term_id":"GO:0005634","term_label":"nucleus","supporting_discovery_ids":[5,8]}],"pathway":[{"term_id":"R-HSA-74160","term_label":"Gene expression (Transcription)","supporting_discovery_ids":[0,2,5]}],"complexes":["RNA polymerase II","Pol II elongation complex (EC*)","Rpb3 subcomplex"],"partners":["RTF1","SPT5","GPN2","RPB10","RPB2","RPB3","TFIIEΒ"],"other_free_text":[]}},"prefetch_data":{"uniprot":{"accession":"P53803","full_name":"DNA-directed RNA polymerases I, II, and III subunit RPABC4","aliases":["ABC10-alpha","DNA-directed RNA polymerase II subunit K","RNA polymerase II 7.0 kDa subunit","RPB7.0","RPB10alpha"],"length_aa":58,"mass_kda":7.0,"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 a small RNAs, such as 5S rRNA and tRNAs, respectively","subcellular_location":"Nucleus; Nucleus, nucleolus","url":"https://www.uniprot.org/uniprotkb/P53803/entry"},"depmap":{"release":"DepMap","has_data":true,"is_common_essential":true,"resolved_as":"","url":"https://depmap.org/portal/gene/POLR2K","classification":"Common Essential","n_dependent_lines":1086,"n_total_lines":1090,"dependency_fraction":0.9963302752293578},"opencell":{"profiled":true,"resolved_as":"","ensg_id":"ENSG00000147669","cell_line_id":"CID000707","localizations":[{"compartment":"nucleolus_fc_dfc","grade":3},{"compartment":"nucleoplasm","grade":2}],"interactors":[{"gene":"GTF2F1","stoichiometry":10.0},{"gene":"INTS14","stoichiometry":10.0},{"gene":"MED19","stoichiometry":10.0},{"gene":"POLR1B","stoichiometry":10.0},{"gene":"POLR1E","stoichiometry":10.0},{"gene":"POLR2A","stoichiometry":10.0},{"gene":"POLR2B","stoichiometry":10.0},{"gene":"POLR2C","stoichiometry":10.0},{"gene":"POLR2D","stoichiometry":10.0},{"gene":"POLR2E","stoichiometry":10.0}],"url":"https://opencell.sf.czbiohub.org/target/CID000707","total_profiled":1310},"omim":[{"mim_id":"621544","title":"GPN-LOOP GTPase 2; GPN2","url":"https://www.omim.org/entry/621544"},{"mim_id":"606033","title":"POLYMERASE II, RNA, SUBUNIT K; POLR2K","url":"https://www.omim.org/entry/606033"},{"mim_id":"606023","title":"POLYMERASE II, RNA, SUBUNIT H; POLR2H","url":"https://www.omim.org/entry/606023"},{"mim_id":"606017","title":"POLYMERASE II, RNA, SUBUNIT D; POLR2D","url":"https://www.omim.org/entry/606017"},{"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":"Nucleoli fibrillar center","reliability":"Supported"}],"tissue_specificity":"Low tissue specificity","tissue_distribution":"Detected in all","driving_tissues":[],"url":"https://www.proteinatlas.org/search/POLR2K"},"hgnc":{"alias_symbol":["RPB10alpha","RPB12"],"prev_symbol":[]},"alphafold":{"accession":"P53803","domains":[{"cath_id":"2.20.28.30","chopping":"14-45","consensus_level":"high","plddt":91.6616,"start":14,"end":45}],"viewer_url":"https://alphafold.ebi.ac.uk/entry/P53803","model_url":"https://alphafold.ebi.ac.uk/files/AF-P53803-F1-model_v6.cif","pae_url":"https://alphafold.ebi.ac.uk/files/AF-P53803-F1-predicted_aligned_error_v6.png","plddt_mean":85.75},"mouse_models":{"mgi_url":"https://www.informatics.jax.org/marker/summary?nomen=POLR2K","jax_strain_url":"https://www.jax.org/strain/search?query=POLR2K"},"sequence":{"accession":"P53803","fasta_url":"https://rest.uniprot.org/uniprotkb/P53803.fasta","uniprot_url":"https://www.uniprot.org/uniprotkb/P53803/entry","alphafold_viewer_url":"https://alphafold.ebi.ac.uk/entry/P53803"}},"corpus_meta":[{"pmid":"32541898","id":"PMC_32541898","title":"Structure of complete Pol II-DSIF-PAF-SPT6 transcription complex reveals RTF1 allosteric activation.","date":"2020","source":"Nature structural & molecular biology","url":"https://pubmed.ncbi.nlm.nih.gov/32541898","citation_count":130,"is_preprint":false},{"pmid":"22753024","id":"PMC_22753024","title":"An in-depth map of polyadenylation sites in cancer.","date":"2012","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/22753024","citation_count":115,"is_preprint":false},{"pmid":"7883169","id":"PMC_7883169","title":"RNA polymerase II subunit RPB9 is required for accurate start site selection.","date":"1995","source":"Genes & development","url":"https://pubmed.ncbi.nlm.nih.gov/7883169","citation_count":97,"is_preprint":false},{"pmid":"17786358","id":"PMC_17786358","title":"Identification of differential expression of genes in hepatocellular carcinoma by suppression subtractive hybridization combined cDNA microarray.","date":"2007","source":"Oncology reports","url":"https://pubmed.ncbi.nlm.nih.gov/17786358","citation_count":94,"is_preprint":false},{"pmid":"18195044","id":"PMC_18195044","title":"The Rpb4 subunit of RNA polymerase II contributes to cotranscriptional recruitment of 3' processing factors.","date":"2008","source":"Molecular and cellular biology","url":"https://pubmed.ncbi.nlm.nih.gov/18195044","citation_count":63,"is_preprint":false},{"pmid":"18237450","id":"PMC_18237450","title":"Tiling resolution array CGH and high density expression profiling of urothelial carcinomas delineate genomic amplicons and candidate target genes specific for advanced tumors.","date":"2008","source":"BMC medical genomics","url":"https://pubmed.ncbi.nlm.nih.gov/18237450","citation_count":59,"is_preprint":false},{"pmid":"11058130","id":"PMC_11058130","title":"Archaeal RNA polymerase subunits F and P are bona fide homologs of eukaryotic RPB4 and RPB12.","date":"2000","source":"Nucleic acids research","url":"https://pubmed.ncbi.nlm.nih.gov/11058130","citation_count":47,"is_preprint":false},{"pmid":"26160718","id":"PMC_26160718","title":"Chlorogenic acid prevents acetaminophen-induced liver injury: the involvement of CYP450 metabolic enzymes and some antioxidant signals.","date":"2015","source":"Journal of Zhejiang University. 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B, Analytical technologies in the biomedical and life sciences","url":"https://pubmed.ncbi.nlm.nih.gov/14698245","citation_count":2,"is_preprint":false},{"pmid":"39558055","id":"PMC_39558055","title":"Integrated analysis of single-cell RNA sequencing and bulk transcriptome data identifies a pyroptosis-associated diagnostic model for Parkinson's disease.","date":"2024","source":"Scientific reports","url":"https://pubmed.ncbi.nlm.nih.gov/39558055","citation_count":1,"is_preprint":false}],"cost":{"stage1":{"model":"claude-sonnet-4-6","input_tokens":18497,"output_tokens":2152,"usd":0.043886,"stage1_stop_reason":"end_turn"},"stage2":{"model":"claude-opus-4-8","input_tokens":9149,"output_tokens":2928,"usd":0.059472,"stage2_stop_reason":"end_turn"},"total_usd":0.103358,"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\": 2020,\n      \"finding\": \"RTF1 Plus3 domain associates with Pol II subunit RPB12 (POLR2K) and the phosphorylated C-terminal region of DSIF subunit SPT5 within the complete Pol II elongation complex (EC*); RTF1 also forms four α-helices extending from the Plus3 domain along the Pol II protrusion and RPB10 to the polymerase funnel, and strongly stimulates Pol II elongation.\",\n      \"method\": \"Cryo-EM structure of complete porcine/human Pol II-DSIF-PAF-SPT6-RTF1 complex\",\n      \"journal\": \"Nature structural & molecular biology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — cryo-EM structure with functional validation (elongation stimulation assay), multiple orthogonal methods in a single rigorous study\",\n      \"pmids\": [\"32541898\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2018,\n      \"finding\": \"Gpn2 interacts directly with Rpb12 (POLR2K ortholog in yeast), and when Gpn2 is functionally defective the assembly of the Rpb3 subcomplex is disrupted, leading to defects in overall RNA polymerase II biogenesis.\",\n      \"method\": \"Co-immunoprecipitation, pulldown, and functional assembly assays in yeast\",\n      \"journal\": \"Molecular and cellular biology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reciprocal interaction demonstrated with defined assembly phenotype, single lab with two orthogonal methods\",\n      \"pmids\": [\"29661922\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2008,\n      \"finding\": \"Archaeal RNA polymerase subunit P (ortholog of eukaryotic Rpb12/POLR2K) is directly or indirectly required for stable open complex formation; the conserved zinc ribbon in the N-terminus is important for proper interaction with other RNA polymerase subunits, and the C-terminal 17-amino-acid peptide is sufficient to support basic RNA polymerase functions in vitro.\",\n      \"method\": \"In vitro transcription reconstitution assays with deletion mutants and cysteine substitutions in archaeal RNAP; complementation of yeast RPB12 deletion with archaeal subunit P\",\n      \"journal\": \"Molecular microbiology\",\n      \"confidence\": \"High\",\n      \"confidence_rationale\": \"Tier 1 / Strong — in vitro reconstitution with mutagenesis and complementation assays providing multiple orthogonal lines of evidence\",\n      \"pmids\": [\"19183282\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2009,\n      \"finding\": \"Archaeal subunit P (Rpb12/POLR2K ortholog) is not required for RNAP assembly per se but is essential for open complex formation; deletion of subunit P abolishes stable open complex formation while preserving the ability to extend a dinucleotide on a premelted template or RNA on an elongation scaffold.\",\n      \"method\": \"Reconstituted archaeal RNAP lacking subunit P tested in promoter-directed initiation, open complex formation, and elongation assays\",\n      \"journal\": \"Biochemical Society transactions\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 1 / Moderate — in vitro reconstitution with defined functional readouts, but single lab and largely consistent with PMID:19183282\",\n      \"pmids\": [\"19143595\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Archaeal RNA polymerase subunit P interacts with other archaeal subunits in a manner predicted from its eukaryotic Rpb12 counterpart; an archaeal-human F-RPB7 hybrid complex can form, demonstrating cross-kingdom functional conservation of the Rpb12 interaction interface.\",\n      \"method\": \"In vitro and in vivo protein interaction assays with recombinant subunits from Methanococcus jannaschii\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — in vitro and in vivo pulldown/interaction assays, single lab with two orthogonal approaches\",\n      \"pmids\": [\"11058130\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2006,\n      \"finding\": \"TbRPB12 (T. brucei ortholog of POLR2K) contains a conserved CX2CX10-15CX2C zinc-binding motif characteristic of eukaryotic RPB12 polypeptides and is a subunit of a transcriptionally active, alpha-amanitin-sensitive RNA polymerase II purified from T. brucei.\",\n      \"method\": \"Affinity purification of RNA Pol II and mass spectrometric identification; in vitro transcription activity assay with alpha-amanitin sensitivity test\",\n      \"journal\": \"Molecular and biochemical parasitology\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical purification with MS identification and functional transcription assay, single lab\",\n      \"pmids\": [\"16962183\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2005,\n      \"finding\": \"S. pombe TFIIEβ subunit binds Rpb12 (POLR2K ortholog) and Rpb2 subunits of Pol II, establishing a direct physical contact between TFIIE and Rpb12 at transcription initiation.\",\n      \"method\": \"In vitro binding/interaction assays between recombinant TFIIE subunits and individual Pol II subunits\",\n      \"journal\": \"Genes to cells : devoted to molecular & cellular mechanisms\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — direct binding assay showing specific interaction, single lab, single method\",\n      \"pmids\": [\"15743411\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2000,\n      \"finding\": \"Rpb12 (POLR2K ortholog) is assembled into the RNA polymerase II complex through multiple subunit-subunit contacts; co-expression experiments in insect cells established the assembly pathway involves Rpb3-mediated recruitment of subunits, with Rpb12 present in the assembled complex.\",\n      \"method\": \"Baculovirus co-expression of Pol II subunits in insect cells followed by sequential affinity chromatography (GST-Rpb3 and His-Rpb1) to isolate subunit complexes\",\n      \"journal\": \"Nucleic acids research\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — reconstitution in insect cells with affinity isolation, single lab\",\n      \"pmids\": [\"10648788\"],\n      \"is_preprint\": false\n    },\n    {\n      \"year\": 2001,\n      \"finding\": \"Rpb12 (POLR2K ortholog) is one of the five subunits shared among RNA polymerases I, II and III in S. pombe; fractionation by glycerol gradient centrifugation showed that some excess Rpb12 exists in unassembled forms outside the Pol II holoenzyme.\",\n      \"method\": \"Quantitative immunoblotting and glycerol gradient centrifugation of whole-cell extracts\",\n      \"journal\": \"European journal of biochemistry\",\n      \"confidence\": \"Medium\",\n      \"confidence_rationale\": \"Tier 2 / Moderate — biochemical fractionation with quantitative analysis, single lab, two orthogonal methods\",\n      \"pmids\": [\"11168400\"],\n      \"is_preprint\": false\n    }\n  ],\n  \"current_model\": \"POLR2K (RPB12) is a small zinc ribbon-containing subunit shared among all three nuclear RNA polymerases that contributes to RNA Pol II complex integrity and elongation: its N-terminal zinc ribbon mediates proper interaction with other polymerase subunits, it is required (directly or indirectly) for stable promoter open complex formation, it serves as a docking site for the RTF1 Plus3 domain within the Pol II elongation complex to allosterically stimulate transcription, and its assembly into the Rpb3 subcomplex is facilitated by the biogenesis factor Gpn2.\"\n}\n```","stage2_raw":"{\n  \"mechanistic_narrative\": \"POLR2K (RPB12) is a small zinc ribbon–containing subunit shared among the nuclear RNA polymerases that contributes to polymerase complex integrity, promoter open complex formation, and transcription elongation [#2, #8]. Its conserved N-terminal zinc ribbon (a CX2CX10-15CX2C motif) mediates proper interaction with other polymerase subunits, while a short C-terminal peptide is sufficient to support basic polymerase function in vitro [#2, #5]. The subunit is incorporated into the polymerase through Rpb3-mediated assembly of subunit subcomplexes, a process facilitated by the biogenesis factor Gpn2, whose loss disrupts Rpb3 subcomplex assembly and overall Pol II biogenesis [#1, #7]. At initiation, POLR2K makes direct physical contact with the TFIIE\\u03b2 subunit and is required—directly or indirectly—for stable open complex formation [#6, #2, #3]. During elongation it serves as a docking site for the RTF1 Plus3 domain within the complete Pol II elongation complex, where RTF1 strongly stimulates Pol II elongation [#0]. Cross-kingdom complementation and hybrid-complex studies show the Rpb12 interaction interface is conserved from archaea to humans [#2, #4].\",\n  \"teleology\": [\n    {\n      \"year\": 2000,\n      \"claim\": \"Established that the Rpb12 interaction interface is functionally conserved across kingdoms and that the subunit engages defined polymerase partners as predicted from its eukaryotic counterpart.\",\n      \"evidence\": \"In vitro and in vivo interaction assays with recombinant Methanococcus jannaschii subunits, including an archaeal-human F-RPB7 hybrid complex\",\n      \"pmids\": [\"11058130\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Did not map the precise residues mediating the interface\", \"No direct test in the human Pol II context\"]\n    },\n    {\n      \"year\": 2000,\n      \"claim\": \"Defined how Rpb12 is incorporated into Pol II, showing it joins the complex through multiple subunit contacts during an Rpb3-mediated assembly pathway.\",\n      \"evidence\": \"Baculovirus co-expression of Pol II subunits in insect cells with sequential GST-Rpb3 and His-Rpb1 affinity chromatography\",\n      \"pmids\": [\"10648788\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Order of Rpb12 entry into the assembly pathway not resolved\", \"No biogenesis factor identified at this stage\"]\n    },\n    {\n      \"year\": 2001,\n      \"claim\": \"Showed Rpb12 is one of five subunits shared among Pol I, II and III and that a free, unassembled pool exists outside the holoenzyme.\",\n      \"evidence\": \"Quantitative immunoblotting and glycerol gradient centrifugation of S. pombe whole-cell extracts\",\n      \"pmids\": [\"11168400\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Function of the unassembled pool unknown\", \"No regulatory role assigned to the shared distribution\"]\n    },\n    {\n      \"year\": 2005,\n      \"claim\": \"Identified a direct initiation-stage contact, showing TFIIE\\u03b2 binds Rpb12, linking the subunit to general transcription factor engagement.\",\n      \"evidence\": \"In vitro binding assays between recombinant S. pombe TFIIE subunits and individual Pol II subunits\",\n      \"pmids\": [\"15743411\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Interaction not validated in an intact preinitiation complex\", \"Functional consequence of the TFIIE\\u03b2-Rpb12 contact not quantified\"]\n    },\n    {\n      \"year\": 2006,\n      \"claim\": \"Confirmed Rpb12 is a bona fide subunit of an active eukaryotic Pol II in a divergent organism, with a conserved zinc-binding motif.\",\n      \"evidence\": \"Affinity purification of T. brucei Pol II with MS identification and alpha-amanitin-sensitive in vitro transcription assay\",\n      \"pmids\": [\"16962183\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No mutational dissection of the zinc motif in this system\", \"Specific mechanistic role within the complex not addressed\"]\n    },\n    {\n      \"year\": 2009,\n      \"claim\": \"Separated the subunit's roles in assembly versus catalysis, demonstrating it is dispensable for RNAP assembly but essential for stable open complex formation.\",\n      \"evidence\": \"Reconstituted archaeal RNAP lacking subunit P tested in initiation, open complex, and elongation assays\",\n      \"pmids\": [\"19143595\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Whether the open-complex requirement is direct or indirect not resolved\", \"Largely overlapping with the same lab's complementary study\"]\n    },\n    {\n      \"year\": 2008,\n      \"claim\": \"Pinpointed structural determinants of function, showing the N-terminal zinc ribbon is needed for subunit interactions while a 17-residue C-terminal peptide suffices for basic polymerase activity, with archaeal subunit P complementing yeast RPB12.\",\n      \"evidence\": \"In vitro transcription reconstitution with deletion/cysteine-substitution mutants and cross-kingdom yeast complementation\",\n      \"pmids\": [\"19183282\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Mechanism by which the subunit enables open complex formation not defined\", \"Not extended to the human Pol II enzyme\"]\n    },\n    {\n      \"year\": 2018,\n      \"claim\": \"Identified a dedicated biogenesis factor, showing Gpn2 binds Rpb12 and is required for Rpb3 subcomplex assembly and overall Pol II biogenesis.\",\n      \"evidence\": \"Co-immunoprecipitation, pulldown, and functional assembly assays in yeast\",\n      \"pmids\": [\"29661922\"],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"Structural basis of the Gpn2-Rpb12 interaction unknown\", \"Whether Gpn2 acts directly on Rpb12 or downstream of it not fully resolved\"]\n    },\n    {\n      \"year\": 2020,\n      \"claim\": \"Defined a discrete elongation function, showing Rpb12 serves as a docking site for the RTF1 Plus3 domain in the complete Pol II elongation complex, coupling this contact to strong elongation stimulation.\",\n      \"evidence\": \"Cryo-EM of the complete porcine/human Pol II-DSIF-PAF-SPT6-RTF1 complex with elongation stimulation assay\",\n      \"pmids\": [\"32541898\"],\n      \"confidence\": \"High\",\n      \"gaps\": [\"Quantitative contribution of the Rpb12 contact alone to RTF1 stimulation not isolated\", \"Regulation of RTF1 docking in vivo not addressed\"]\n    },\n    {\n      \"year\": null,\n      \"claim\": \"How the human POLR2K zinc ribbon mechanistically enables open complex formation and how its assembly, initiation, and elongation roles are coordinated in vivo remain unresolved.\",\n      \"evidence\": \"\",\n      \"pmids\": [],\n      \"confidence\": \"Medium\",\n      \"gaps\": [\"No structural mechanism linking Rpb12 to open complex stability\", \"No in vivo dissection of separable functions in human cells\"]\n    }\n  ],\n  \"mechanism_profile\": {\n    \"molecular_activity\": [\n      {\"term_id\": \"GO:0005198\", \"supporting_discovery_ids\": [0, 2, 7]},\n      {\"term_id\": \"GO:0140098\", \"supporting_discovery_ids\": [2, 3, 5]}\n    ],\n    \"localization\": [\n      {\"term_id\": \"GO:0005634\", \"supporting_discovery_ids\": [5, 8]}\n    ],\n    \"pathway\": [\n      {\"term_id\": \"R-HSA-74160\", \"supporting_discovery_ids\": [0, 2, 5]}\n    ],\n    \"complexes\": [\n      \"RNA polymerase II\",\n      \"Pol II elongation complex (EC*)\",\n      \"Rpb3 subcomplex\"\n    ],\n    \"partners\": [\n      \"RTF1\",\n      \"SPT5\",\n      \"Gpn2\",\n      \"RPB10\",\n      \"Rpb2\",\n      \"Rpb3\",\n      \"TFIIE\\u03b2\"\n    ],\n    \"other_free_text\": []\n  }\n}","audit_flag":null,"evaluation":{"pairwise":"win","faith_supported":6,"faith_total":6,"faith_pct":100.0}}