Affinage

POLR2I

DNA-directed RNA polymerase II subunit RPB9 · UniProt P36954

Length
125 aa
Mass
14.5 kDa
Annotated
2026-06-10
25 papers in source corpus 20 papers cited in narrative 20 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

POLR2I (RPB9) is a conserved, non-essential subunit of RNA polymerase II that integrates transcription start site selection, elongation fidelity, and transcription-coupled DNA repair into the polymerase's catalytic cycle (PMID:7883169, PMID:9169440, PMID:12411509). At initiation, RPB9 directs accurate start site selection, and recombinant protein add-back fully rescues the upstream start-site shifts seen on its deletion; this function reflects functional interactions with the general transcription factors TFIIB and TFIIF and contributes to recruitment of TFIIE to the polymerase (PMID:7883169, PMID:8692696, PMID:14522989, PMID:11779853). During elongation, RPB9 controls transcriptional fidelity in the active center by delaying premature trigger-loop closure on incoming NTP—an effect mediated through its C-terminal domain contacting the Rpb1 trigger loop and anchoring of Rpb1 helix α21—so that its loss elevates misincorporation and error propagation in vivo and in vitro (PMID:19439405, PMID:27226557, PMID:16492753, PMID:24099331). RPB9 is also required for TFIIS-mediated transcript cleavage and read-through of arrest sites, linking proofreading to elongation competence (PMID:9169440, PMID:24099331). These elongation activities feed a dedicated, Rad26-independent subpathway of transcription-coupled DNA repair that requires the Zn1 and linker domains, while a separate Zn2-dependent activity promotes UV-induced ubiquitylation and proteasomal degradation of Rpb1 (PMID:12411509, PMID:17030604, PMID:17452455). Beyond core transcription, RPB9 activates ATG1/ULK1 transcription through the transcription factor Gcn4 to support autophagy (PMID:36102592), and depletion of zebrafish polr2i disrupts cardiac development with phenotypes rescued by polr2i mRNA (PMID:41198546).

Mechanistic history

Synthesis pass · year-by-year structured walk · 15 steps
  1. 1991 Medium

    Established that RPB9 is a genuine but dispensable Pol II subunit, defining the question of what specialized function a non-essential polymerase subunit serves.

    Evidence Gene deletion and genetic growth assays in yeast

    PMID:1918023

    Open questions at the time
    • Does not identify the molecular step RPB9 acts on
    • Conditional growth phenotype not mechanistically explained
  2. 1995 High

    Showed RPB9 governs accurate transcription start site selection, assigning it a defined role at initiation rather than general mRNA synthesis.

    Evidence Deletion plus in vitro reconstitution with recombinant add-back and metal-binding domain mutagenesis

    PMID:7883169

    Open questions at the time
    • Does not define which general factors mediate the effect
    • Structural basis of start-site shift unresolved
  3. 1996 Medium

    Placed RPB9 in a genetic circuit with TFIIB, indicating start-site selection is set by Rpb9-TFIIB cooperation in the preinitiation complex.

    Evidence Genetic suppressor screen with defined alleles and in vivo start site analysis

    PMID:8692696

    Open questions at the time
    • Genetic interaction does not prove direct physical contact
    • C-terminal truncation effect not structurally mapped
  4. 1997 High

    Resolved RPB9's elongation role: it restrains read-through at arrest sites and is required for TFIIS-stimulated reactivation, coupling the subunit to proofreading.

    Evidence In vitro elongation and TFIIS stimulation assays with recombinant RPB9 reconstitution

    PMID:9169440

    Open questions at the time
    • Does not define the domain or contact mediating TFIIS dependence
    • In vivo relevance to fidelity not yet shown
  5. 2000 High

    Dissected RPB9 domains, assigning the linker to Pol II docking and the C-terminal zinc ribbon acidic loop to elongation activity.

    Evidence Site-directed mutagenesis and deletion analysis with in vitro elongation assays

    PMID:10644677 PMID:10938084

    Open questions at the time
    • Separable initiation versus elongation functions not yet linked to repair
    • Single-domain stimulation failure mechanism unclear
  6. 2002 High

    Defined an Rpb9-mediated transcription-coupled repair subpathway distinct from Rad26 and showed Rpb9 contributes to TFIIE recruitment, broadening its role to repair and PIC assembly.

    Evidence Single/double deletion strand-specific UV repair assays; yeast two-hybrid and co-IP for TFIIE

    PMID:11779853 PMID:12411509

    Open questions at the time
    • TFIIE interaction shown by two-hybrid/co-IP without reciprocal structural validation
    • Mechanistic link between elongation and the TCR subpathway not yet established
  7. 2003 High

    Identified impaired Pol II-TFIIF interaction in Rpb9-deficient polymerase as the basis for upstream start-site shifts, connecting the initiation defect to a specific factor contact.

    Evidence Reconstituted transcription with purified factors and gel mobility shift assays

    PMID:14522989

    Open questions at the time
    • Does not resolve whether the TFIIF contact is direct or polymerase-conformation mediated
  8. 2006 Medium

    Demonstrated in vivo error-prone transcription on RPB9 loss and mapped TCR and elongation to the shared Zn1/linker domains, establishing elongation competence as a prerequisite for the Rpb9 repair subpathway.

    Evidence In vivo fidelity assay with cDNA sequencing; domain-deletion UV repair and elongation assays; promoter-element mutagenesis

    PMID:16492753 PMID:17023424 PMID:17030604

    Open questions at the time
    • Molecular signal coupling elongation to repair not defined
    • SAGA dependence of the subpathway not mechanistically explained
  9. 2007 Medium

    Assigned the Zn2 domain a distinct role in UV-triggered Rpb1 ubiquitylation and proteasomal degradation, separating a damage-response function from the elongation/repair functions.

    Evidence UV irradiation, western blot for ubiquitylation/degradation, domain deletion, co-IP and proteasome inhibition

    PMID:17452455

    Open questions at the time
    • The ubiquitin ligase recruited via Zn2 not identified
    • Single-lab co-IP for Pol II interaction
  10. 2013 High

    Provided a unified active-center mechanism: RPB9 delays NTP sequestration by acting on the trigger loop, controlling both misincorporation and error propagation and enabling TFIIS cleavage.

    Evidence Pre-steady state kinetics, NTP misincorporation and TFIIS cleavage assays, genetic synthetic lethality with rpb1 trigger-loop alleles

    PMID:19439405 PMID:24099331

    Open questions at the time
    • Direct structural contact between Rpb9 C-terminus and trigger loop not solved
    • No effect on NTP selectivity leaves selection step unexplained
  11. 2016 Medium

    Refined the active-center model to an indirect mechanism in which Rpb9 anchors Rpb1 helix α21 to modulate trigger-loop mobility, explaining its kinetic effects.

    Evidence Genetic suppressor screen, mutagenesis, in vitro elongation and misincorporation assays, α-amanitin epistasis

    PMID:27226557

    Open questions at the time
    • Anchoring interaction inferred genetically/biochemically without a structure
    • Quantitative contribution to in vivo fidelity unclear
  12. 2021 Medium

    Extended RPB9 function to small-RNA biogenesis, showing the C. elegans ortholog recruits the Integrator complex to drive piRNA gene termination and silencing.

    Evidence C. elegans knockout, co-IP for Integrator recruitment, genetic epistasis and piRNA sequencing

    PMID:33533030

    Open questions at the time
    • Whether the Integrator-recruitment role is conserved beyond C. elegans untested
    • Single-lab co-IP without reciprocal validation
  13. 2022 Medium

    Identified a promoter-specific gene-regulatory role: Rpb9 activates ATG1/ULK1 transcription via Gcn4 to control autophagy, conserved to mammalian cells.

    Evidence KO library screen, ChIP for promoter binding, qRT-PCR, autophagy flux, mammalian knockdown

    PMID:36102592

    Open questions at the time
    • How a core Pol II subunit confers gene-selective activation not explained
    • Direct versus Gcn4-dependent recruitment not fully separated
  14. 2018 Medium

    Linked Rpb9 to genome stability through DNA damage checkpoint activation and a synthetic dependence on histone H3 acetylation for double-strand break repair.

    Evidence Double-mutant analysis, checkpoint marker western blots, viability and chromosome segregation microscopy

    PMID:29440683

    Open questions at the time
    • Mechanism by which Rpb9 supports checkpoint signaling unresolved
    • Connection to its transcription/TCR roles not established
  15. 2025 Medium

    Established an organismal requirement for POLR2I in vertebrate cardiac development, with mRNA rescue confirming specificity.

    Evidence Morpholino knockdown with mRNA rescue and cardiac functional/imaging readouts in zebrafish

    PMID:41198546

    Open questions at the time
    • Which transcriptional function underlies the cardiac phenotype unknown
    • Mitochondrial quality defect mechanistically uncharacterized

Open questions

Synthesis pass · forward-looking unresolved questions
  • It remains unresolved how the distinct domain-specific activities of POLR2I (initiation, elongation fidelity, TCR, Rpb1 degradation, gene-selective activation) are coordinated within an intact organism and whether the conserved cardiac and autophagy roles reflect a single underlying transcriptional defect.
  • No structural model of human POLR2I within Pol II in the corpus
  • Tissue-specific transcriptional targets in vertebrates undefined

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140098 catalytic activity, acting on RNA 3 GO:0005198 structural molecule activity 2 GO:0060089 molecular transducer activity 2 GO:0140110 transcription regulator activity 2
Localization
GO:0005634 nucleus 2
Pathway
R-HSA-73894 DNA Repair 3 R-HSA-74160 Gene expression (Transcription) 3 R-HSA-1266738 Developmental Biology 1 R-HSA-8953854 Metabolism of RNA 1 R-HSA-9612973 Autophagy 1
Partners
GCN4RPB1TFIIBTFIIETFIIFTFIIS
Complex memberships
RNA polymerase II

Evidence

Reading pass · 20 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1991 RPB9 is a non-essential subunit of RNA polymerase II required for normal cell growth over a wide temperature range; deletion produces heat- and cold-sensitive cells but does not abolish mRNA synthesis. Gene deletion/disruption, genetic growth assays The Journal of biological chemistry Medium 1918023
1995 RPB9 is required for accurate transcription start site selection by RNA polymerase II; deletion causes upstream shifts to new or previously minor start sites at multiple promoters in vivo and in vitro, and addition of recombinant RPB9 fully rescues the initiation defect in vitro. RPB9 gene deletion, in vitro transcription reconstitution, recombinant protein add-back, site-directed mutagenesis of metal-binding domain Genes & development High 7883169
1996 RPB9 (SSU73) functionally interacts with TFIIB in transcription start site selection; the ssu73-1 allele (nonsense at codon 107, truncating the C-terminal 16 aa) suppresses both the growth defect and downstream start site shift caused by the sua7-1 TFIIB mutation, establishing a functional interaction between Rpb9 and TFIIB during preinitiation complex formation. Genetic suppressor screen, allele isolation and sequencing, in vivo start site analysis Nucleic acids research Medium 8692696
1997 RPB9 promotes transcription elongation through DNA arrest sites and is required for TFIIS-mediated read-through; RNA polymerase II lacking RPB9 (pol IIDelta9) elongates more efficiently through pause/arrest sequences but cannot be reactivated by TFIIS; addition of recombinant RPB9 to pol IIDelta9 restores wild-type elongation properties. In vitro transcription elongation assay, biochemical reconstitution with recombinant RPB9, TFIIS stimulation assay The Journal of biological chemistry High 9169440
2000 The C-terminal zinc ribbon acidic loop of RPB9 is critical for transcription elongation activity; the conserved linker region (residues 89-95, DPTLPR) mediates interaction with RNA polymerase II; individual zinc ribbon domains in isolation cannot stimulate transcription by pol IIDelta9. Site-directed mutagenesis, deletion analysis, in vitro transcription elongation assay The Journal of biological chemistry High 10644677
2000 RPB9 has a synthetic phenotype with the TFIIS gene (DST1) for 6-azauracil sensitivity; overexpression of TFIIS partially suppresses the 6-AU sensitivity of rpb9Δ cells; the N-terminal zinc ribbon restores wild-type initiation start sites but does not complement elongation-specific growth defects, indicating separable functions of the two domains. Genetic epistasis (double deletion), drug sensitivity assay, high-copy suppression, domain complementation in vivo, genome-wide transcription profiling The Journal of biological chemistry Medium 10938084
2002 RPB9 mediates a subpathway of transcription-coupled DNA repair (TCR) in S. cerevisiae that is independent of Rad26 and operates more effectively in the coding region; simultaneous deletion of RPB9 and RAD26 completely abolishes TCR, indicating these are the only two TCR subpathways in RNA Pol II-transcribed genes; RPB4 suppresses the RPB9-mediated TCR subpathway. Gene deletion (single and double mutants), UV-induced DNA damage repair assay (strand-specific), genetic epistasis The EMBO journal High 12411509
2002 Rpb9 physically interacts with Tfa1, the largest subunit of TFIIE, via a two-hybrid interaction; co-immunoprecipitation of TFIIE with RNA polymerase II is strongly reduced in rpb9Δ, indicating Rpb9 contributes to TFIIE recruitment to the polymerase; rpb9 mutations are synthetically lethal with loss of Elongator or SAGA histone acetyltransferase activity. Yeast two-hybrid, co-immunoprecipitation, synthetic lethality analysis The Journal of biological chemistry Medium 11779853
2003 RNA polymerase II lacking Rpb9 has an impaired interaction with TFIIF (Tfg1-Tfg2 complex), and this impaired interaction is associated with upstream shifts in mRNA 5'-end positions in reconstituted transcription assays with purified general transcription factors. Reconstituted in vitro transcription with purified factors, gel mobility shift assay, recombinant holo-TFIIF production The Journal of biological chemistry High 14522989
2006 The Zn1 and linker domains of Rpb9 are essential for both transcription elongation and TCR functions; the Zn2 domain is dispensable for these functions; impairment of transcription elongation completely abolishes Rpb9-mediated TCR, suggesting the elongation function of Rpb9 is required for TCR. Domain deletion mutagenesis, UV repair assay (strand-specific), transcription elongation assay in vivo Molecular and cellular biology Medium 17030604
2006 RPB9-mediated TCR is strictly transcription-coupled and requires both TATA and UAS sequences; its efficiency depends on the SAGA complex; Rad26-mediated repair operates differently and can function independently of transcription when transcription levels are too low. Promoter element deletion/mutation, strand-specific UV repair assay, genetic analysis of SAGA complex The Journal of biological chemistry Medium 17023424
2006 Deletion of RPB9 in yeast results in error-prone transcription in vivo, as measured by increased read-through of a nonsense allele (can1-100); rpb9Δ strains have increased steady-state levels of can1-100 mRNA and sequence analysis of cDNAs confirmed significantly increased transcriptional substitutions and insertions. In vivo transcription fidelity assay (canavanine sensitivity), cDNA sequencing, Northern blot Proceedings of the National Academy of Sciences of the United States of America Medium 16492753
2007 In response to UV radiation, Rpb9 promotes ubiquitylation and degradation of Rpb1 (the largest Pol II subunit) via the 26S proteasome; the Zn2 domain is essential for this function while Zn1 and linker play subsidiary roles; co-immunoprecipitation shows that near-full-length Rpb9 is required for strong interaction with core Pol II. UV irradiation, western blot for ubiquitylation and degradation, domain deletion mutagenesis, co-immunoprecipitation, proteasome inhibitor treatment Molecular and cellular biology Medium 17452455
2009 RPB9 controls transcription fidelity by delaying NTP sequestration in the RNA polymerase II active center; RPB9 deletion promotes premature closure of the trigger loop on incoming NTP prior to phosphodiester bond formation, enhancing NTP misincorporation and mismatch extension; this is mediated by interaction between the C-terminal domain of Rpb9 and the trigger loop of Rpb1. In vitro NTP misincorporation assay, pre-steady state kinetic analysis, synthetic lethality with rpb1-E1103G, comparison of wild-type and rpb9Δ polymerases The Journal of biological chemistry High 19439405
2013 In the absence of Rpb9, the rate of error propagation (extending a mismatched RNA 3' end) is increased 2-3 fold in multiple sequence contexts; TFIIS-mediated error excision rate and extent are also significantly compromised without Rpb9; Rpb9 facilitates formation of a conformation necessary for RNA cleavage by TFIIS. No effect of Rpb9 on NTP selectivity was observed. In vitro transcription elongation assay with mismatched RNA, competition kinetics, TFIIS-stimulated cleavage assay Biochemistry High 24099331
2016 Rpb9 indirectly modulates trigger loop (TL) mobility by anchoring the position of Rpb1 α-helix 21 (α21), which directly interacts with the TL during opening and closing; missense alleles of RPB9 that suppress rpb1-G730D (α21 substitution) confirm this structural relationship; disruption of proposed anchoring interactions in Rpb9 or Rpb1 results in increased elongation rate in vitro and phenotypes shared by rpb9Δ strains; α-amanitin (TL mobility inhibitor) suppresses the effect of Rpb9 loss on NTP misincorporation. Genetic suppressor screen, site-directed mutagenesis, in vitro elongation rate assay, NTP misincorporation assay, epistasis analysis of double mutants The Journal of biological chemistry Medium 27226557
2021 In C. elegans, the RNA Pol II core subunit RPB-9 is required for piRNA biogenesis by recruiting the Integrator complex to piRNA genes, thereby promoting transcriptional termination; loss of rpb-9 impairs piRNA-mediated gene silencing and heritable silencing at DNA transposon families. Genetic screen (C. elegans KO), biochemical co-immunoprecipitation, genetic epistasis, piRNA sequencing The EMBO journal Medium 33533030
2018 Rpb9-deficient yeast cells show defective DNA damage checkpoint activation (reduced γH2A and Rad53 signaling); histone H3 N-terminal lysine acetylation becomes essential for DNA double-strand break repair and viability in the absence of Rpb9; combined loss leads to genomic instability and aberrant chromosome segregation. Genetic double-mutant analysis, western blot for checkpoint markers (γH2A, Rad53), cell viability assay, microscopy for chromosome segregation Scientific reports Medium 29440683
2022 The RNA polymerase II subunit Rpb9 specifically activates ATG1 transcription by binding to the ATG1 promoter region in a manner mediated by the transcription factor Gcn4; Rpb9 deficiency reduces autophagic activity; this function is conserved in mammalian cells where Rpb9 regulates ULK1 (ATG1 ortholog) transcription. High-throughput KO library screen, ChIP (promoter binding), qRT-PCR, autophagy flux assay, mammalian cell knockdown EMBO reports Medium 36102592
2025 Knockdown of polr2i in zebrafish disrupts cardiac development, causing elongated heart tubes with reduced chamber overlap, pericardial edema, reduced ejection fraction and cardiac output, disrupted left-right asymmetry of heart/liver/pancreas, and impaired mitochondrial quality in myocardial cells; these phenotypes are rescued by co-injection of polr2i mRNA, confirming specificity. Morpholino-mediated knockdown in zebrafish, mRNA rescue experiments, transgenic fluorescent reporter lines, cardiac functional measurements, hemoglobin staining Frontiers in bioscience (Landmark edition) Medium 41198546

Source papers

Stage 0 corpus · 25 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2002 Rpb4 and Rpb9 mediate subpathways of transcription-coupled DNA repair in Saccharomyces cerevisiae. The EMBO journal 109 12411509
1997 Transcription elongation through DNA arrest sites. A multistep process involving both RNA polymerase II subunit RPB9 and TFIIS. The Journal of biological chemistry 101 9169440
1995 RNA polymerase II subunit RPB9 is required for accurate start site selection. Genes & development 97 7883169
1991 Yeast RNA polymerase II subunit RPB9 is essential for growth at temperature extremes. The Journal of biological chemistry 86 1918023
2000 RNA polymerase II subunit Rpb9 regulates transcription elongation in vivo. The Journal of biological chemistry 82 10938084
2009 Rpb9 subunit controls transcription fidelity by delaying NTP sequestration in RNA polymerase II. The Journal of biological chemistry 72 19439405
2006 RNA polymerase II subunit Rpb9 is important for transcriptional fidelity in vivo. Proceedings of the National Academy of Sciences of the United States of America 69 16492753
1996 Functional interaction between TFIIB and the Rpb9 (Ssu73) subunit of RNA polymerase II in Saccharomyces cerevisiae. Nucleic acids research 56 8692696
2002 The Rpb9 subunit of RNA polymerase II binds transcription factor TFIIE and interferes with the SAGA and elongator histone acetyltransferases. The Journal of biological chemistry 51 11779853
2011 Point mutations in the Rpb9-homologous domain of Rpc11 that impair transcription termination by RNA polymerase III. Nucleic acids research 32 21450810
2007 Yeast Rpb9 plays an important role in ubiquitylation and degradation of Rpb1 in response to UV-induced DNA damage. Molecular and cellular biology 30 17452455
2000 Yeast RNA polymerase II subunit RPB9. Mapping of domains required for transcription elongation. The Journal of biological chemistry 29 10644677
2021 The RNA polymerase II subunit RPB-9 recruits the integrator complex to terminate Caenorhabditis elegans piRNA transcription. The EMBO journal 25 33533030
2013 Fidelity of RNA polymerase II transcription: Role of Rpb9 [corrected] in error detection and proofreading. Biochemistry 25 24099331
2006 Evidence that the transcription elongation function of Rpb9 is involved in transcription-coupled DNA repair in Saccharomyces cerevisiae. Molecular and cellular biology 24 17030604
2003 Yeast RNA polymerase II lacking the Rpb9 subunit is impaired for interaction with transcription factor IIF. The Journal of biological chemistry 24 14522989
2016 RNA Polymerase II Trigger Loop Mobility: INDIRECT EFFECTS OF Rpb9. The Journal of biological chemistry 17 27226557
1998 Identification of the gene and the protein of RNA polymerase II subunit 9 (Rpb9) from the fission yeast Schizosacharomyces pombe. Gene 17 9852944
2006 Modulation of Rad26- and Rpb9-mediated DNA repair by different promoter elements. The Journal of biological chemistry 11 17023424
2018 Rpb9-deficient cells are defective in DNA damage response and require histone H3 acetylation for survival. Scientific reports 9 29440683
2022 The RNA polymerase II subunit Rpb9 activates ATG1 transcription and autophagy. EMBO reports 5 36102592
2021 Deletion of the non-essential Rpb9 subunit of RNA polymerase II results in pleiotropic phenotypes in Schizosaccharomyces pombe. Biochimica et biophysica acta. Proteins and proteomics 3 33775921
2022 Absence of the Rpb9 subunit of RNA polymerase II reduces the chronological life span in fission yeast. Journal of basic microbiology 2 35618649
2025 polr2i is Required for Zebrafish Early Cardiac Development. Frontiers in bioscience (Landmark edition) 0 41198546
2000 [Chromosomal localization of rpb9+ and tfa1+ genes, coding for components of the mRNA synthesis apparatus of Schizosaccharomyces pombe]. Bioorganicheskaia khimiia 0 11041002

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