Affinage

POLR2H

DNA-directed RNA polymerases I, II, and III subunit RPABC3 · UniProt P52434

Length
150 aa
Mass
17.1 kDa
Annotated
2026-06-10
48 papers in source corpus 13 papers cited in narrative 14 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 6/6 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POLR2H (RPB8/hRPB17) is an essential, single-copy subunit shared by all three nuclear RNA polymerases (I, II, and III), incorporated into each enzyme as a structural component required for viability (PMID:2186966, PMID:22149079). It adopts an eight-stranded antiparallel beta-barrel with an unstructured omega-loop, classifying it as an OB-fold protein, and the human protein binds single-stranded DNA nonspecifically (PMID:9461075, PMID:16632472). Within the polymerase, RPB8 docks onto the pore-1 module of the largest subunit (Rpb1/Rpa190/Rpc160) through its invariant GGLLM motif, and functionally cooperates with RPB6, with which it makes direct contact in the assembled enzyme (PMID:11486042, PMID:9642054). During RNA polymerase II biogenesis it forms a cytoplasmic assembly intermediate with Rpb1 that engages the HSP90 cochaperone RPAP3 and the R2TP/Prefoldin-like complex, coupling subunit assembly to a quality-control step that licenses nuclear import (PMID:20864038). Beyond its constitutive structural role, RPB8 is polyubiquitinated by the BRCA1-BARD1 ubiquitin ligase in response to UV and chemotherapeutic DNA damage; this modification does not trigger degradation but increases soluble RPB8 and is required for cell survival, as ubiquitination-deficient cells become UV-hypersensitive with elevated caspase activity (PMID:17283126). Assembly of the enzyme follows a defined order in which RPB11 promotes the RPB3-RPB8 interaction and RPB8 in turn enhances the RPB1-RPB3 interaction (PMID:10648788).

Mechanistic history

Synthesis pass · year-by-year structured walk · 11 steps
  1. 1990 High

    Established that RPB8 is not a polymerase-II-specific factor but a single essential subunit physically shared by all three nuclear RNA polymerases, defining its core identity.

    Evidence Gene isolation, reciprocal immunoprecipitation, and tetrad viability analysis in S. cerevisiae

    PMID:2186966

    Open questions at the time
    • Does not resolve the structural basis of incorporation
    • Stoichiometry and contacts within each polymerase not defined
  2. 1995 High

    Showed the human and yeast subunits are functionally interchangeable, establishing cross-species conservation while revealing partial divergence via a thermosensitive phenotype.

    Evidence Heterospecific complementation of a yeast rpb8 null with human RPB8

    PMID:7651387

    Open questions at the time
    • Molecular basis of the thermosensitivity not identified
    • Does not map the divergent surfaces
  3. 1998 High

    Defined the fold of RPB8 as an OB-fold beta-barrel, providing the structural framework for understanding its binding surfaces and a candidate nucleic-acid-binding activity.

    Evidence NMR solution structure of yeast RPB8

    PMID:9461075

    Open questions at the time
    • Function of the omega-loop unresolved
    • Ligand of the OB-fold not yet demonstrated
  4. 1998 Medium

    Mapped RPB8 contacts within the assembled polymerase and revealed species-specific genetic coupling to the RNAP III largest subunit, hinting at differential roles across the three enzymes.

    Evidence Far-Western, cross-linking, and heterospecific complementation/dosage suppression in S. pombe and S. cerevisiae

    PMID:9642054 PMID:9927738

    Open questions at the time
    • Single-lab cross-linking contacts
    • Why S. pombe Rpb8 selectively impairs RNAP III assembly is unexplained
  5. 2000 Medium

    Reconstituted a sequential assembly pathway showing how RPB8 incorporation is ordered relative to RPB3 and RPB11, and localized the endogenous protein to nucleoli and nucleoplasm in a transcription-dependent manner.

    Evidence Recombinant insect-cell co-expression with affinity chromatography; immunofluorescence with transcriptional inhibitors

    PMID:10623476 PMID:10648788

    Open questions at the time
    • In vitro assembly may not capture in vivo chaperone requirements
    • Redistribution mechanism upon inhibition not defined
  6. 2001 Medium

    Identified the GGLLM motif as the determinant of RPB8 binding to the pore-1 module of all three large subunits and demonstrated functional interplay with RPB6, linking a specific surface to enzyme function.

    Evidence Two-hybrid assays, site-directed mutagenesis, and dosage-suppressor genetics in yeast

    PMID:11486042

    Open questions at the time
    • Two-hybrid interactions not confirmed structurally in context
    • Mechanism of RPB6 suppression unresolved
  7. 2006 High

    Determined the human RPB8 structure and demonstrated nonspecific single-stranded DNA binding, assigning a possible nucleic-acid-contacting activity to the human subunit.

    Evidence NMR structure determination, biochemical DNA-binding assays, and NMR titration

    PMID:16632472

    Open questions at the time
    • Physiological relevance of ssDNA binding within the holoenzyme unknown
    • Sequence preference and in vivo target not established
  8. 2007 High

    Connected RPB8 to the DNA-damage response, showing BRCA1-BARD1 polyubiquitinates it to increase the soluble pool and promote survival rather than to target it for degradation.

    Evidence Proteomics, Co-IP, in vitro/in vivo ubiquitination, K→R mutagenesis, and stable cell-line phenotyping in HeLa

    PMID:17283126

    Open questions at the time
    • Downstream fate of the soluble ubiquitinated pool unclear
    • How increased soluble RPB8 promotes survival mechanistically unresolved
  9. 2010 High

    Placed RPB8 in a cytoplasmic RNA Pol II assembly intermediate coupled to HSP90/RPAP3/R2TP chaperone-driven quality control, defining how assembly is linked to nuclear import.

    Evidence Quantitative MS proteomics, HSP90 inhibition, nuclear fractionation, and microscopy

    PMID:20864038

    Open questions at the time
    • Order of RPB8 entry into the cytoplasmic intermediate not specified
    • Direct chaperone-RPB8 contacts not mapped
  10. 2012 Medium

    Validated RPB8 as a tractable shared bait that simultaneously captures all three human polymerases and reports its live-cell localization, consolidating its pan-polymerase membership in human cells.

    Evidence HaloTag affinity purification with label-free quantitative proteomics and imaging

    PMID:22149079

    Open questions at the time
    • Novel partners not functionally characterized
    • Single-lab dataset
  11. 2025 Medium

    Implicated RPB8 as a functional mediator of GLS1-dependent RNA Pol II regulation in a hepatic disease context, expanding its role beyond a passive structural subunit.

    Evidence Reciprocal Co-IP, hepatic overexpression/knockdown in vivo, and truncation-mutant rescue in an alcohol-induced steatosis model

    PMID:40936098

    Open questions at the time
    • Mechanism by which POLR2H abolishes GLS1 protection unresolved
    • Single-lab study in one disease model

Open questions

Synthesis pass · forward-looking unresolved questions
  • How RPB8's distinct activities — pore-1 anchoring, ssDNA binding, BRCA1-BARD1 ubiquitination, and chaperone-coupled assembly — are integrated to differentially regulate the three polymerases remains unresolved.
  • No unified model linking ubiquitination to assembly/survival
  • Functional consequence of ssDNA binding in the holoenzyme unknown
  • Polymerase-specific roles of RPB8 not dissected in human cells

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0003677 DNA binding 1
Localization
GO:0005654 nucleoplasm 1 GO:0005730 nucleolus 1 GO:0005829 cytosol 1
Pathway
R-HSA-74160 Gene expression (Transcription) 2 R-HSA-392499 Metabolism of proteins 1 R-HSA-73894 DNA Repair 1
Partners
BARD1BRCA1GLS1POLR2APOLR2CPOLR2EPOLR2FRPAP3
Complex memberships
R2TP/Prefoldin-like complexRNA polymerase IRNA polymerase IIRNA polymerase III

Evidence

Reading pass · 14 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1990 RPB8 (POLR2H) is a shared subunit present in all three yeast nuclear RNA polymerases (I, II, and III); the gene is single-copy, essential for viability, and immunoprecipitation of RPB6 co-precipitates proteins consistent with RNA Pol I, II, and III subunits, confirming shared incorporation. Gene isolation/sequencing, immunoprecipitation, sporulation/tetrad analysis Genes & development High 2186966
1995 Human RPB8 (hRPB17/POLR2H) functionally complements the S. cerevisiae rpb8-Δ1 null mutant, demonstrating cross-species functional conservation, though with a strong thermosensitive phenotype indicating partial functional divergence. Heterospecific complementation of yeast null mutant Molecular and cellular biology High 7651387
1998 The solution structure of yeast RPB8 (POLR2H ortholog) was determined by NMR and revealed an eight-stranded antiparallel beta-barrel with a large unstructured omega-loop, classifying it as a novel member of the oligonucleotide/oligosaccharide (OB)-binding protein family. NMR spectroscopy (solution structure determination) Nature structural biology High 9461075
2001 Rpb8p interacts via its invariant GGLLM motif with a fragment conserved in the largest subunits of RNA polymerases I (Rpa190p), II (Rpb1p), and III (Rpc160p) corresponding to the pore 1 module; defective mutants at the GGLLM motif and two other conserved residues all impair this two-hybrid interaction. Two-hybrid interaction assay, site-directed mutagenesis Molecular and cellular biology Medium 11486042
2001 Rpb6p and Rpb8p functionally interact in vivo: increased gene dosage of Rpb6p suppresses the conditional growth defect caused by replacing Rpb8p with its human counterpart, and also suppresses an RNA polymerase I mutant (rpa190-G728D) at the pore 1 module. Genetic suppression (dosage suppressor analysis) in yeast Molecular and cellular biology Medium 11486042
1998 S. pombe Rpb8 cannot substitute for S. cerevisiae ABC14.5 (Rpb8) in vivo; amino acid differences in the N-terminal 67 residues are responsible for this functional distinction. Overexpression of Rpc1 (C160, largest RNAP III subunit) allows S. pombe rpb8 to functionally replace ABC14.5, revealing a specific genetic interaction between Rpb8 and the RNAP III largest subunit. S. pombe rpb8 selectively impairs RNA polymerase III but not RNA polymerase I complex assembly. Heterospecific complementation, dosage suppressor analysis, biochemical assembly analysis Nucleic acids research Medium 9927738
2000 In assembly experiments using baculovirus-expressed subunits, Rpb8 was incorporated into a seven-subunit complex containing Rpb1, Rpb2, Rpb3, Rpb5, Rpb7, Rpb8, and Rpb11. Rpb11 enhances Rpb3-Rpb8 interaction, and Rpb8 in turn enhances Rpb1-Rpb3 interaction, defining a sequential assembly mechanism. Recombinant co-expression in insect cells, GST and His-tag affinity chromatography Nucleic acids research Medium 10648788
1998 Far-Western blot analysis of S. pombe RNA polymerase II showed Rpb8 weakly interacts with Rpb5 and/or Rpb11 (a 15-kDa subunit), in addition to direct contacts with large subunits Rpb1 and Rpb2. Cross-linking experiments confirmed Rpb6-Rpb8 direct contact within the assembled polymerase. Far-Western blot, protein-protein cross-linking with bifunctional cross-linkers Journal of molecular biology Medium 9642054
2006 The three-dimensional solution structure of human RPB8 (hRPB8/POLR2H) was determined by NMR, revealing an eight-stranded beta-barrel, six short helices, and an unstructured Omega-loop belonging to the OB-fold family. hRPB8 has a more clustered positively charged interface with RPB1 compared to yeast RPB8. hRPB8 binds single-stranded DNA nonspecifically, with identified residues involved in binding and conformational changes upon DNA binding. NMR spectroscopy (structure determination), biochemical DNA-binding assays, NMR titration The Journal of biological chemistry High 16632472
2007 BRCA1-BARD1 ubiquitin ligase complex mediates polyubiquitination of RPB8 (POLR2H) in response to DNA damage (UV irradiation and epirubicin). RPB8 physically interacts with BRCA1-BARD1. This ubiquitination does not destabilize RPB8 but increases soluble RPB8. Substitution of five lysine residues abolishing ubiquitination while preserving polymerase activity results in UV hypersensitivity and upregulated caspase activity in stable HeLa lines, indicating ubiquitination is required for cell survival after DNA damage. Proteomics screen, Co-immunoprecipitation, in vitro and in vivo ubiquitination assay, site-directed mutagenesis (K→R), stable cell line phenotyping, RNAi knockdown Cancer research High 17283126
2010 POLR2H (Rpb8) and Rpb1 form a cytoplasmic assembly intermediate associated with the HSP90 cochaperone hSpagh (RPAP3) and the R2TP/Prefoldin-like complex during RNA polymerase II biogenesis. HSP90 activity stabilizes incompletely assembled Rpb1 in the cytoplasm, and nuclear import of Rpb1 requires the presence of all subunits, indicating quality-control coupling of assembly to nuclear import. MS-based quantitative proteomics, characterization of assembly intermediates, HSP90 inhibition, nuclear fractionation, fluorescence microscopy Molecular cell High 20864038
2012 POLR2H (HaloTag-fused) simultaneously captures human RNA polymerases I, II, and III as confirmed by quantitative proteomics, identifying all RNAP core subunits and novel interacting partners, and the fusion protein reports POLR2H subcellular localization in live cells. HaloTag affinity purification, label-free quantitative proteomics, cellular imaging Journal of proteome research Medium 22149079
2000 Immunofluorescence with monoclonal antibodies against RPB8 (shared by all three polymerases) reveals its localization to nucleoli and nucleoplasm in human cells, with redistribution upon treatment with transcriptional inhibitors DRB and actinomycin D, linking RPB8 localization to active transcription. Immunofluorescence with validated monoclonal antibodies, transcriptional inhibitor treatment Experimental cell research Medium 10623476
2025 GLS1 (glutaminase 1) acts as a chaperone that interacts with POLR2H and POLR2E subunits to modulate the RNA pol II complex in the nucleus; overexpression of POLR2H (full-length but not truncated variants) abolishes GLS1's protective effects against alcohol-induced hepatic steatosis, placing POLR2H as a functional mediator of GLS1-dependent RNA pol II complex regulation. Co-immunoprecipitation (POLR2H-GLS1 interaction), hepatic overexpression/knockdown in vivo, truncation mutant analysis Advanced science Medium 40936098

Source papers

Stage 0 corpus · 48 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2010 HSP90 and its R2TP/Prefoldin-like cochaperone are involved in the cytoplasmic assembly of RNA polymerase II. Molecular cell 238 20864038
1996 In vivo degradation of RNA polymerase II largest subunit triggered by alpha-amanitin. Nucleic acids research 224 8760875
1990 Subunits shared by eukaryotic nuclear RNA polymerases. Genes & development 164 2186966
1995 Four subunits that are shared by the three classes of RNA polymerase are functionally interchangeable between Homo sapiens and Saccharomyces cerevisiae. Molecular and cellular biology 108 7651387
2009 Evolution of complex RNA polymerases: the complete archaeal RNA polymerase structure. PLoS biology 95 19419240
2005 RNA emerging from the active site of RNA polymerase II interacts with the Rpb7 subunit. Nature structural & molecular biology 86 16327806
2008 Early evolution of eukaryotic DNA-dependent RNA polymerases. Trends in genetics : TIG 49 18384908
1990 RNA polymerase II subunit RPB10 is essential for yeast cell viability. The Journal of biological chemistry 46 2211663
2020 Comparative Study of Organoids from Patient-Derived Normal and Tumor Colon and Rectal Tissue. Cancers 38 32824266
2007 BRCA1 ubiquitinates RPB8 in response to DNA damage. Cancer research 37 17283126
2018 Identification of the key genes and pathways in prostate cancer. Oncology letters 36 30405806
2007 Diversification of function by different isoforms of conventionally shared RNA polymerase subunits. Molecular biology of the cell 35 17267688
2007 Orthologs of the small RPB8 subunit of the eukaryotic RNA polymerases are conserved in hyperthermophilic Crenarchaeota and "Korarchaeota". Biology direct 34 18081935
2006 Purification of an eight subunit RNA polymerase I complex in Trypanosoma brucei. Molecular and biochemical parasitology 33 16730080
2007 Structure of an archaeal RNA polymerase. Journal of molecular biology 31 18164030
2006 Characterization of the RNA polymerase II and III complexes in Leishmania major. International journal for parasitology 31 17275824
2006 Characterization of RNA polymerase II subunits of Trypanosoma brucei. Molecular and biochemical parasitology 29 16621069
2001 Partners of Rpb8p, a small subunit shared by yeast RNA polymerases I, II and III. Molecular and cellular biology 29 11486042
1998 Two large subunits of the fission yeast RNA polymerase II provide platforms for the assembly of small subunits. Journal of molecular biology 29 9642054
2012 Structural and functional analyses of the interaction of archaeal RNA polymerase with DNA. Nucleic acids research 28 22848102
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
1996 Molecular assembly of RNA polymerase II from the fission yeast Schizosaccharomyces pombe: subunit-subunit contact network involving Rpb5. Genes to cells : devoted to molecular & cellular mechanisms 25 9077438
1998 Eukaryotic RNA polymerase subunit RPB8 is a new relative of the OB family. Nature structural biology 24 9461075
1997 Gene organization and protein sequence of the small subunits of Schizosaccharomyces pombe RNA polymerase II. Gene 24 9322754
2000 Functional conservation of RNA polymerase II in fission and budding yeasts. Journal of molecular biology 23 10653691
2012 Examining the complexity of human RNA polymerase complexes using HaloTag technology coupled to label free quantitative proteomics. Journal of proteome research 22 22149079
2000 Involvement of multiple subunit-subunit contacts in the assembly of RNA polymerase II. Nucleic acids research 20 10648788
1999 Sequence divergence of the RNA polymerase shared subunit ABC14.5 (Rpb8) selectively affects RNA polymerase III assembly in Saccharomyces cerevisiae. Nucleic acids research 19 9927738
2000 Isolation and characterization of monoclonal antibodies directed against subunits of human RNA polymerases I, II, and III. Experimental cell research 18 10623476
2024 Transcriptome and proteomic analysis of mpox virus F3L-expressing cells. Frontiers in cellular and infection microbiology 13 38415010
2023 miR-624 accelerates the growth of liver cancer cells by inhibiting EMC3. Non-coding RNA research 12 37810370
2006 Structural, biochemical, and dynamic characterizations of the hRPB8 subunit of human RNA polymerases. The Journal of biological chemistry 12 16632472
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 12 11168594
2021 Identification of novel candidate genes for age at first calving in Nellore cows using a SNP chip specifically developed for Bos taurus indicus cattle. Theriogenology 11 34392169
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
2022 Evaluation of autoantibody signatures in pituitary adenoma patients using human proteome arrays. Proteomics. Clinical applications 8 35939377
1996 Sequence and analysis of a 33 kb fragment from the right arm of chromosome XV of the yeast Saccharomyces cerevisiae. Yeast (Chichester, England) 6 8840505
2023 Identification of novel N7-methylguanine-related gene signatures associated with ulcerative colitis and the association with biological therapy. Inflammation research : official journal of the European Histamine Research Society ... [et al.] 5 37889323
2019 Molecular characterization of a RNA polymerase (RNAP) II (DNA directed) polypeptide H (POLR2H) in Pacific white shrimp (Litopenaeus vannamei) and its role in response to high-pH stress. Fish & shellfish immunology 5 31830564
1999 DNA sequencing and analysis of a 67.4 kb region from the right arm of Schizosaccharomyces pombe chromosome II reveals 28 open reading frames including the genes his5, pol5, ppa2, rip1, rpb8 and skb1. Yeast (Chichester, England) 5 10407269
1998 [Structural-functional characteristics of the Schizosaccharomyces pombe rpb8+ gene, coding the subunit of RNA polymerase I-III, specific only for eukaryotes]. Bioorganicheskaia khimiia 4 10335407
2012 Molecular characterization of a gene POLR2H encoded an essential subunit for RNA polymerase II from the Giant Panda (Ailuropoda Melanoleuca). Molecular biology reports 3 23070920
2024 Exploration of common pathogenesis and candidate hub genes between HIV and monkeypox co-infection using bioinformatics and machine learning. Scientific reports 2 39496786
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 GLS1-RNA Polymerase II Axis Mediates Glutamine-Dependent Hepatoprotective Effects on Alcoholic Liver Disease in High-Protein Diets. Advanced science (Weinheim, Baden-Wurttemberg, Germany) 1 40936098
2026 De Novo 3q27.1 Microdeletion Refines the Critical Region and Implicates PSMD2 Haploinsufficiency in Growth and Neurodevelopmental Abnormalities. American journal of medical genetics. Part A 0 41804662
2024 Transcriptional genes of lysosome-associated membrane protein 2A in sciatic nerve injuries by bioinformatics. Neuroreport 0 38935077
1999 [Molecular evolution and structure of eukaryotic nuclear RNA polymerase subunits in light of the exon-intron organization of their genes]. Bioorganicheskaia khimiia 0 10645488

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