Affinage

POLR2K

DNA-directed RNA polymerases I, II, and III subunit RPABC4 · UniProt P53803

Round 2 corrected
Length
58 aa
Mass
7.0 kDa
Annotated
2026-04-28
63 papers in source corpus 16 papers cited in narrative 16 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POLR2K (RPB12/RPABC4) is a small, conserved zinc ribbon-containing subunit shared by all three eukaryotic RNA polymerases (I, II, and III) that is essential for promoter open complex formation but dispensable for overall polymerase assembly (PMID:19183282, PMID:19143595). Structurally embedded in the Pol II core, POLR2K serves as a docking platform for the elongation factor RTF1 (via its Plus3 domain) during processive transcription elongation and directly contacts the general transcription factor TFIIEβ at initiation, thereby contributing to both stages of the transcription cycle (PMID:32541898, PMID:15743411). During RNAPII biogenesis, POLR2K interacts with the assembly chaperone Gpn2 to nucleate the Rpb3 subcomplex, and it participates with Rpb10 in an early co-translational assembly platform for RNAPI and RNAPIII (PMID:29661922, PMID:34055890). POLR2K is maintained at stoichiometric excess over other Pol II subunits, with a substantial free (unassembled) pool in the nucleus (PMID:11168400).

Mechanistic history

Synthesis pass · year-by-year structured walk · 8 steps
  1. 2000 High

    Determination of the Pol II crystal structure established that Rpb12/POLR2K is a bona fide structural subunit of the polymerase core, resolving its position within the 10-subunit enzyme architecture and demonstrating conservation across all three eukaryotic RNA polymerases.

    Evidence X-ray crystallography of yeast Pol II at 3 Å resolution

    PMID:10784442

    Open questions at the time
    • Atomic-resolution side-chain details for Rpb12 not resolved at this stage
    • Functional role of Rpb12 within the core not addressed
  2. 2000 High

    Cross-kingdom complementation showed that archaeal subunit P is a functional homolog of POLR2K, establishing deep evolutionary conservation of the zinc ribbon-containing subunit and validating archaeal systems as models for dissecting Rpb12 function.

    Evidence Recombinant archaeal–human hybrid complex reconstitution and in vitro/in vivo interaction assays

    PMID:11058130

    Open questions at the time
    • Whether functional interchangeability extends to all transcription stages was untested
  3. 2001 High

    Quantitative protein and mRNA measurements revealed that Rpb12 is present at ~10-fold molar excess over core Pol II subunits, with a significant unassembled nuclear pool, raising the question of whether excess Rpb12 has functions beyond the assembled polymerase.

    Evidence Quantitative immunoblotting, glycerol gradient sedimentation, GFP-fusion microscopy, and competitive RT-PCR in S. pombe

    PMID:11168400 PMID:11168594

    Open questions at the time
    • Biological significance of the free Rpb12 pool remains undefined
    • Whether excess extends to mammalian cells is unknown
  4. 2005 Medium

    Direct binding between Rpb12 and TFIIEβ positioned POLR2K as a contact point for general transcription machinery at promoters during initiation, providing the first specific protein–protein interaction linking Rpb12 to the pre-initiation complex.

    Evidence Protein–protein binding assays and ChIP in S. pombe

    PMID:15743411

    Open questions at the time
    • Structural basis of the Rpb12–TFIIEβ interface not determined
    • Functional consequence of disrupting this interaction on transcription initiation not tested
    • Single-lab observation without independent replication
  5. 2008 High

    Reconstitution and in vivo complementation experiments demonstrated that Rpb12/subunit P is specifically required for promoter open complex formation but not for polymerase assembly or RNA extension on premelted templates, identifying its precise mechanistic contribution to the transcription cycle.

    Evidence Archaeal RNAP reconstitution lacking subunit P, open complex assays, cysteine mutagenesis of the zinc ribbon, yeast RPB12-deletion rescue

    PMID:19143595 PMID:19183282

    Open questions at the time
    • Mechanism by which Rpb12 promotes DNA melting is unclear
    • Whether the 17-amino-acid C-terminal peptide sufficiency observed in vitro holds in vivo
  6. 2018 High

    The discovery that the GTPase-related chaperone Gpn2 directly binds Rpb12 to nucleate the Rpb3 subcomplex defined a specific role for POLR2K in RNAPII biogenesis, distinct from its role in the assembled enzyme.

    Evidence Reciprocal Co-IP, GST pull-down, and siRNA knockdown with RNAPII assembly readout in human/yeast cells

    PMID:29661922

    Open questions at the time
    • Structural detail of the Gpn2–Rpb12 interface not resolved
    • Whether Gpn2 chaperones Rpb12 into RNAPI/III as well is untested
  7. 2020 High

    Cryo-EM of the complete Pol II elongation complex revealed that RTF1's Plus3 domain directly docks on RPB12, establishing POLR2K as a structural platform for recruitment of the PAF1 complex component RTF1 and its stimulation of Pol II elongation.

    Evidence Cryo-EM structure of porcine/human EC* at near-atomic resolution, elongation assays, RTF1 latch-deletion mutagenesis

    PMID:32541898

    Open questions at the time
    • Whether RTF1–RPB12 contact is regulated by post-translational modifications is unknown
    • Allosteric mechanism by which RTF1 latch stimulates translocation not fully defined
  8. 2021 Medium

    Evidence that Rpb12 and Rpb10 form a co-translational assembly platform for RNAPI/III biogenesis, stimulated by Rbs1-mediated RPB10 mRNA regulation, extended the biogenesis role of POLR2K beyond Pol II to all three nuclear RNA polymerases.

    Evidence Genetic and biochemical analysis of RNAP assembly factors, mRNA-binding assays, structural modeling in yeast

    PMID:34055890

    Open questions at the time
    • Co-translational assembly model partly inferred; direct visualization of nascent-chain interactions lacking
    • Whether this mechanism operates in mammalian cells is untested

Open questions

Synthesis pass · forward-looking unresolved questions
  • The mechanism by which Rpb12's zinc ribbon promotes DNA strand separation during open complex formation remains structurally unresolved, and the biological function of the large free (unassembled) Rpb12 pool is unknown.
  • No high-resolution structure of the open complex transition state showing Rpb12 contacts with melted DNA
  • Free Rpb12 pool function unexplored
  • Post-translational regulation of POLR2K not characterized

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 4
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-74160 Gene expression (Transcription) 5
Partners
GPN2POLR2CPOLR2EPOLR2JRTF1TFIIE
Complex memberships
RNA polymerase IRNA polymerase IIRNA polymerase III

Evidence

Reading pass · 16 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
2000 A backbone model of 10-subunit yeast RNA polymerase II was derived from X-ray crystallographic data at 3 Å resolution. Nine of the ten subunits, including the Rpb12 (POLR2K) subunit, are conserved among the three eukaryotic RNA polymerases. The structure reveals that Rpb12 is a bona fide structural component of the Pol II core, contributing to the overall polymerase architecture. X-ray crystallography at 3 Å resolution of yeast Pol II Science High 10784442
2000 The archaeal RNA polymerase subunit P is a functional homolog of eukaryotic Rpb12 (POLR2K). Recombinant M. jannaschii subunit P and subunit F (Rpb4 homolog) interact with other archaeal RNAP subunits in a manner paralleling eukaryotic RPB12 interactions, including formation of an archaeal-human F-RPB7 hybrid complex in vitro. This demonstrated conservation of the zinc ribbon-containing Rpb12/P subunit across the archaeal-eukaryotic divide. In vitro and in vivo protein interaction assays with recombinant archaeal and human subunits; hybrid complex reconstitution Nucleic acids research High 11058130
2001 In S. pombe, Rpb12 (POLR2K ortholog) is the most abundant of all 12 Pol II subunits intracellularly, present at ~10-fold higher levels than the three core subunits (Rpb1, Rpb2, Rpb3). Glycerol gradient centrifugation showed that some Rpb12 exists in unassembled (free) forms in the cell, distinct from the fully assembled Pol II enzyme. GFP-fusion microscopy confirmed nuclear localization. Quantitative immunoblotting, glycerol gradient centrifugation, GFP-fusion fluorescence microscopy European journal of biochemistry High 11168400
2001 mRNA levels for the 12 S. pombe Pol II subunit genes were quantified by competitive PCR. Rpb12 (POLR2K ortholog) mRNA is among the most abundant of the rpb transcripts. Importantly, protein-to-mRNA ratios revealed that Rpb12 protein is present in large excess relative to its mRNA, indicating highly efficient translation or protein stability. Quantitative competitive PCR, oligo capping for transcription start site mapping Genes to cells Medium 11168594
2002 The intracellular concentration of Rpb12 (POLR2K ortholog), like all other Pol II subunits in S. pombe, remains constant across different phases and rates of cell growth. The relative stoichiometry among all 12 subunits is also maintained constant, implying that the concentration of the assembled Pol II holoenzyme is tightly regulated. Quantitative immunoblotting across multiple growth conditions (exponential, stationary, stress phases) Genes to cells Medium 11918671
2004 Rpb12 (POLR2K ortholog) from S. pombe was heterologously overexpressed in E. coli as a hexahistidine fusion and purified to near-homogeneity by metal-chelate affinity chromatography and gel filtration. Identity confirmed by MALDI-TOF mass spectrometry. This established that isolated recombinant Rpb12 is biochemically tractable for physicochemical studies. Recombinant protein expression in E. coli, affinity chromatography, gel filtration, MALDI-TOF mass spectrometry Journal of chromatography B Medium 14698245
2005 In S. pombe, the TFIIEβ subunit of the general transcription factor TFIIE was shown to directly bind the Rpb12 (POLR2K ortholog) subunit of Pol II. This interaction positions TFIIE at promoters in vivo and implicates Rpb12 as a contact point for the general transcription machinery at the initiation stage. Protein-protein interaction binding specificity assays, chromatin immunoprecipitation (ChIP) for in vivo localization Genes to cells Medium 15743411
2006 T. brucei RNA polymerase II was purified by affinity chromatography and shown to be transcriptionally active in promoter-independent and promoter-dependent in vitro assays and sensitive to α-amanitin. Mass spectrometric analysis identified TbRPB12 (POLR2K ortholog) as a genuine subunit of the trypanosomal Pol II, containing the conserved CX₂CX₁₀₋₁₅CX₂C zinc-binding motif characteristic of eukaryotic RPB12 polypeptides. Affinity chromatography purification, in vitro transcription assay, α-amanitin sensitivity assay, mass spectrometry identification Molecular and biochemical parasitology High 16962183
2008 Archaeal subunit P (Rpb12/POLR2K ortholog) is functionally interchangeable with eukaryotic Rpb12 in vivo and in vitro: archaeal P complemented lethal deletion of RPB12 in yeast, and yeast Rpb12 restored activity of the archaeal ΔP RNAP in reconstitution assays. The ΔP archaeal enzyme failed to form stable open complexes but could extend RNA on premelted templates, establishing that subunit P/Rpb12 is specifically required for promoter opening. Mutation of cysteine residues in the zinc ribbon impaired enzyme activity, and a 17-amino-acid C-terminal peptide was sufficient for all basic RNAP functions in vitro. In vivo complementation (yeast deletion rescue), in vitro reconstitution of archaeal RNAP, open complex formation assays, mutagenesis of zinc ribbon cysteines, transcription assays on premelted templates Molecular microbiology High 19183282
2008 TAP-tagging of Rpb12 (POLR2K ortholog) at its C-terminus in S. cerevisiae caused severe growth defects and morphological abnormalities, indicating that the C-terminus of Rpb12 is critical for its protein interactions and cellular function. This was distinct from the Rpb7-TAP phenotype and demonstrated that Rpb12 engages in interactions through its C-terminal region that are essential for normal cell-cycle progression. TAP-tag insertion at C-terminus as mutagenic tool, cell growth rate measurement, cell morphology analysis Journal of microbiology and biotechnology Low 18467854
2009 Reconstitution studies with archaeal RNAP demonstrated that subunit P (Rpb12/POLR2K ortholog) is not required for RNAP assembly per se but is essential for open complex formation. Conversely, subunit H (Rpb5 ortholog) is needed for all assays except promoter recruitment. Both eukaryotic Rpb12 and Rpb5 can be incorporated into archaeal RNAP and functionally complement their archaeal counterparts in in vitro transcription. Subunit reconstitution of archaeal RNAP lacking specific subunits, open complex formation assays, promoter-directed transcription assays Biochemical Society transactions High 19143595
2018 Two assembly factors, Gpn2 and Rba50, directly participate in the biogenesis of RNA polymerase II by assembling the Rpb3 subcomplex. Gpn2 was shown to interact directly with Rpb12 (POLR2K) by co-immunoprecipitation and pull-down assays. Functional deficiency in Gpn2 disrupted assembly of the Rpb3 subcomplex and impaired overall RNAPII biogenesis, establishing Gpn2 as a chaperone that acts through Rpb12 to nucleate the Rpb3 subcomplex. Co-immunoprecipitation, GST pull-down, siRNA knockdown with assembly phenotype readout Molecular and cellular biology High 29661922
2020 Cryo-EM structure of the complete porcine/human Pol II elongation complex (EC*) containing DSIF, PAF1 complex, SPT6, and RTF1 reveals that the RTF1 Plus3 domain directly contacts Pol II subunit RPB12 (POLR2K). Specifically, RTF1 associates with RPB12 and the phosphorylated C-terminal region of DSIF subunit SPT5, and RTF1's helical extensions contact RPB10 and reach to the polymerase funnel. RTF1 strongly stimulates Pol II elongation, and this requires its 'latch' element, suggesting allosteric activation of Pol II translocation. Cryo-EM structure determination of the complete EC* complex; functional elongation assays; latch deletion mutagenesis Nature structural & molecular biology High 32541898
2021 In yeast RNAPI and RNAPIII biogenesis, Rpb12 (POLR2K) together with Rpb10 forms part of the assembly platform with Rpc40 and Rpc19 (the αα-like heterodimer). It is proposed that this platform is co-translationally seeded during Rpb10 synthesis, and that Rbs1 protein stimulates Rpb10 translation by binding the 3'-UTR of RPB10 mRNA to facilitate assembly of Rpc19-Rpc40, suggesting Rpb12 participates in an early co-translational RNAP assembly event. Genetic and biochemical analysis of RNAP assembly, mRNA-binding protein function assays, structural modeling Frontiers in molecular biosciences Medium 34055890
2022 OpenCell endogenous tagging and live-cell imaging of human POLR2K demonstrated its nuclear localization, consistent with its role as a Pol II subunit. Mass spectrometry-based interaction data confirmed its incorporation into the RNA polymerase II complex in human cells. CRISPR-based endogenous GFP tagging, confocal live-cell imaging, affinity-purification mass spectrometry Science Medium 35271311
2015 Large-scale biochemical fractionation combined with quantitative mass spectrometry across diverse metazoan species confirmed POLR2K (Rpb12) as an ancient, conserved subunit of the RNA polymerase II complex, present in co-complex with other Pol II subunits across all metazoan models examined. Biochemical fractionation, quantitative mass spectrometry co-fractionation across multiple species Nature Medium 26344197

Source papers

Stage 0 corpus · 63 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2012 Insights into RNA biology from an atlas of mammalian mRNA-binding proteins. Cell 1718 22658674
2002 Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proceedings of the National Academy of Sciences of the United States of America 1479 12477932
1998 A novel CDK9-associated C-type cyclin interacts directly with HIV-1 Tat and mediates its high-affinity, loop-specific binding to TAR RNA. Cell 1086 9491887
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
1997 Purification and cDNA cloning of the AdoMet-binding subunit of the human mRNA (N6-adenosine)-methyltransferase. RNA (New York, N.Y.) 869 9409616
2020 A reference map of the human binary protein interactome. Nature 849 32296183
1996 The general transcription factors of RNA polymerase II. Genes & development 849 8946909
2002 Comprehensive proteomic analysis of the human spliceosome. Nature 725 12226669
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
2008 Genome-scale RNAi screen for host factors required for HIV replication. Cell host & microbe 627 18976975
2004 SMYD3 encodes a histone methyltransferase involved in the proliferation of cancer cells. Nature cell biology 595 15235609
2000 Architecture of RNA polymerase II and implications for the transcription mechanism. Science (New York, N.Y.) 452 10784442
2011 HIV latency. Cold Spring Harbor perspectives in medicine 439 22229121
2004 The status, quality, and expansion of the NIH full-length cDNA project: the Mammalian Gene Collection (MGC). Genome research 438 15489334
2022 OpenCell: Endogenous tagging for the cartography of human cellular organization. Science (New York, N.Y.) 432 35271311
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
1999 HIV-1 tat transcriptional activity is regulated by acetylation. The EMBO journal 361 10545121
2012 HIV-1 reverse transcription. Cold Spring Harbor perspectives in medicine 315 23028129
1995 Lentivirus Tat proteins specifically associate with a cellular protein kinase, TAK, that hyperphosphorylates the carboxyl-terminal domain of the large subunit of RNA polymerase II: candidate for a Tat cofactor. Journal of virology 311 7853496
2011 Human mediator subunit MED26 functions as a docking site for transcription elongation factors. Cell 281 21729782
2004 A set of consensus mammalian mediator subunits identified by multidimensional protein identification technology. Molecular cell 265 15175163
2012 The BET bromodomain inhibitor JQ1 activates HIV latency through antagonizing Brd4 inhibition of Tat-transactivation. Nucleic acids research 254 23087374
1996 Enhanced processivity of RNA polymerase II triggered by Tat-induced phosphorylation of its carboxy-terminal domain. Nature 245 8934526
2000 Tat modifies the activity of CDK9 to phosphorylate serine 5 of the RNA polymerase II carboxyl-terminal domain during human immunodeficiency virus type 1 transcription. Molecular and cellular biology 227 10866664
2018 Mapping the Genetic Landscape of Human Cells. Cell 225 30033366
2015 A deep proteomics perspective on CRM1-mediated nuclear export and nucleocytoplasmic partitioning. eLife 198 26673895
2003 The RNA polymerase II elongation complex. Annual review of biochemistry 194 12676794
1992 HIV-1 Tat acts as a processivity factor in vitro in conjunction with cellular elongation factors. Genes & development 193 1559613
2000 Domains in the SPT5 protein that modulate its transcriptional regulatory properties. Molecular and cellular biology 188 10757782
2020 Structure of complete Pol II-DSIF-PAF-SPT6 transcription complex reveals RTF1 allosteric activation. Nature structural & molecular biology 128 32541898
2012 An in-depth map of polyadenylation sites in cancer. Nucleic acids research 115 22753024
1995 RNA polymerase II subunit RPB9 is required for accurate start site selection. Genes & development 96 7883169
2007 Identification of differential expression of genes in hepatocellular carcinoma by suppression subtractive hybridization combined cDNA microarray. Oncology reports 94 17786358
2008 The Rpb4 subunit of RNA polymerase II contributes to cotranscriptional recruitment of 3' processing factors. Molecular and cellular biology 63 18195044
2008 Tiling resolution array CGH and high density expression profiling of urothelial carcinomas delineate genomic amplicons and candidate target genes specific for advanced tumors. BMC medical genomics 59 18237450
2000 Archaeal RNA polymerase subunits F and P are bona fide homologs of eukaryotic RPB4 and RPB12. Nucleic acids research 47 11058130
2015 Chlorogenic acid prevents acetaminophen-induced liver injury: the involvement of CYP450 metabolic enzymes and some antioxidant signals. Journal of Zhejiang University. Science. B 43 26160718
2020 Prediction of breast cancer proteins involved in immunotherapy, metastasis, and RNA-binding using molecular descriptors and artificial neural networks. Scientific reports 41 32444848
2006 Biochemical characterization of Trypanosoma brucei RNA polymerase II. Molecular and biochemical parasitology 36 16962183
2007 Diversification of function by different isoforms of conventionally shared RNA polymerase subunits. Molecular biology of the cell 34 17267688
2001 Intracellular contents and assembly states of all 12 subunits of the RNA polymerase II in the fission yeast Schizosaccharomyces pombe. European journal of biochemistry 27 11168400
2016 The role of tumor metabolism as a driver of prostate cancer progression and lethal disease: results from a nested case-control study. Cancer & metabolism 25 27980733
1997 Gene organization and protein sequence of the small subunits of Schizosaccharomyces pombe RNA polymerase II. Gene 24 9322754
2018 Gpn2 and Rba50 Directly Participate in the Assembly of the Rpb3 Subcomplex in the Biogenesis of RNA Polymerase II. Molecular and cellular biology 23 29661922
2000 Involvement of multiple subunit-subunit contacts in the assembly of RNA polymerase II. Nucleic acids research 20 10648788
2021 Specific Features of RNA Polymerases I and III: Structure and Assembly. Frontiers in molecular biosciences 19 34055890
2016 Selection and validation of reference genes for normalization of quantitative real-time reverse transcription PCR analysis in Poria cocos (Schw.) Wolf (Fuling). Chinese medicine 19 26937250
2006 The fission yeast Rpb4 subunit of RNA polymerase II plays a specialized role in cell separation. Molecular genetics and genomics : MGG 18 16972065
2022 Reprogramming barriers in bovine cells nuclear transfer revealed by single-cell RNA-seq analysis. Journal of cellular and molecular medicine 17 35971640
2008 The archaeal RNA polymerase subunit P and the eukaryotic polymerase subunit Rpb12 are interchangeable in vivo and in vitro. Molecular microbiology 14 19183282
2024 Bioinformatic validation and machine learning-based exploration of purine metabolism-related gene signatures in the context of immunotherapeutic strategies for nonspecific orbital inflammation. Frontiers in immunology 12 38605967
2002 Level of the RNA polymerase II in the fission yeast stays constant but phosphorylation of its carboxyl terminal domain varies depending on the phase and rate of cell growth. Genes to cells : devoted to molecular & cellular mechanisms 11 11918671
2001 Transcription organization and mRNA levels of the genes for all 12 subunits of the fission yeast RNA polymerase II. Genes to cells : devoted to molecular & cellular mechanisms 11 11168594
2009 Mutational studies of archaeal RNA polymerase and analysis of hybrid RNA polymerases. Biochemical Society transactions 9 19143595
2005 Studies of Schizosaccharomyces pombe TFIIE indicate conformational and functional changes in RNA polymerase II at transcription initiation. Genes to cells : devoted to molecular & cellular mechanisms 9 15743411
2019 Genome-wide transcriptional response to altered levels of the Rpb7 subunit of RNA polymerase II identifies its role in DNA damage response in Schizosaccharomyces pombe. FEMS yeast research 3 30395243
2008 A novel approach to investigating protein/protein interactions and their functions by TAP-tagged yeast strains and its application to examine yeast transcription machinery. Journal of microbiology and biotechnology 3 18467854
2023 Association between heat shock factor protein 4 methylation and colorectal cancer risk and potential molecular mechanisms: A bioinformatics study. World journal of gastrointestinal oncology 2 38173437
2022 Absence of the Rpb9 subunit of RNA polymerase II reduces the chronological life span in fission yeast. Journal of basic microbiology 2 35618649
2004 Heterologous overexpression and purification of four common subunits of nuclear RNA polymerases I, II and III of Schizosaccharomyces pombe. Journal of chromatography. B, Analytical technologies in the biomedical and life sciences 2 14698245
2025 Protective effect of energized structured water on bioenergetic function and oxidative stress in H9c2 cells. Explore (New York, N.Y.) 1 40768905
2024 Integrated analysis of single-cell RNA sequencing and bulk transcriptome data identifies a pyroptosis-associated diagnostic model for Parkinson's disease. Scientific reports 1 39558055