Affinage

POLR3C

DNA-directed RNA polymerase III subunit RPC3 · UniProt Q9BUI4

Round 2 corrected
Length
534 aa
Mass
60.6 kDa
Annotated
2026-04-28
60 papers in source corpus 7 papers cited in narrative 7 extracted findings

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POLR3C (RPC32) is a dedicated subunit of the RNA polymerase III initiation-specific heterotrimer (RPC32/RPC39/RPC62) that is essential for promoter-dependent transcription of tRNA, 5S rRNA, and other Pol III gene classes. The heterotrimer dissociates from the Pol III core under denaturing conditions and, when added back, restores specific transcription initiation, with RPC39 bridging TFIIIB and TFIIIC to direct the polymerase to promoters (PMID:9171375, PMID:10523658). Structurally, POLR3C acts as a molecular bridge within the heterotrimer by contacting the eWH and coiled-coil domains of RPC62, and the subcomplex is tethered to the Pol III core via a human-specific iron-sulfur cluster (PMID:26394183, PMID:33558764). Heterozygous loss-of-function mutations in POLR3C cause impaired RNA Pol III-dependent cytosolic DNA sensing with defective interferon induction, conferring susceptibility to severe varicella zoster virus infection (PMID:28783042).

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 1997 High

    Establishing that POLR3C resides in a Pol III-specific subcomplex required for promoter-dependent initiation resolved how Pol III distinguishes initiation from elongation at a subunit level.

    Evidence Immunopurification and reconstituted in vitro transcription with recombinant RPC32/RPC39/RPC62 subcomplex in human cell-free systems

    PMID:9171375

    Open questions at the time
    • Structural basis of how the subcomplex contacts the Pol III core was unknown
    • Individual contributions of RPC32 versus RPC39/RPC62 to initiation were not separated
  2. 1999 Medium

    Demonstrating that TFIIIC90 contacts RPC39 and RPC62 within the POLR3C-containing subcomplex provided a physical mechanism linking TFIIIC recognition of internal promoter elements to Pol III recruitment.

    Evidence Immunodepletion, reciprocal immunoprecipitation, and in vitro interaction assays

    PMID:10523658

    Open questions at the time
    • Whether POLR3C itself makes direct contacts with TFIIIC was not tested
    • Stoichiometry of the TFIIIC–subcomplex interaction was not determined
  3. 2015 High

    Solving the crystal structure of the RPC62–POLR3C binary complex revealed that POLR3C bridges multiple domains of RPC62 and exposes solvent-facing residues, defining its architectural role within the heterotrimer.

    Evidence X-ray crystallography of human RPC62–RPC32β complex fitted into Pol III EM density

    PMID:26394183

    Open questions at the time
    • The structure lacked the third subunit RPC39, leaving the complete heterotrimer architecture unresolved
    • Functional validation of solvent-exposed interaction surfaces was not performed
  4. 2017 High

    Identifying heterozygous POLR3C mutations in patients with severe VZV infection, and rescuing the IFN-induction defect with wild-type allele, established a non-canonical role for Pol III-dependent DNA sensing in antiviral innate immunity.

    Evidence Primary patient leukocyte functional assays measuring IFN induction and viral replication, with lentiviral rescue

    PMID:28783042

    Open questions at the time
    • Whether the immune phenotype reflects a specific POLR3C function beyond its role in the heterotrimer is unknown
    • Genotype–phenotype correlation across additional POLR3C variants remains unexplored
  5. 2021 High

    Near-atomic cryo-EM structures of human Pol III revealed a human-specific iron-sulfur cluster that tethers the POLR3C-containing heterotrimer to the core, explaining a key structural divergence from yeast Pol III.

    Evidence Cryo-EM at 2.8–3.3 Å resolution of unbound and transcribing human Pol III

    PMID:33558764

    Open questions at the time
    • Functional consequences of disrupting the iron-sulfur cluster have not been tested
    • How disease mutations mapped onto the structure alter initiation kinetics is unknown
  6. 2024 Medium

    Functional conservation of the POLR3C ortholog in trypanosomatids confirmed its essential role in Pol III transcription across deeply divergent eukaryotes, while revealing lineage-specific differences such as the absence of a C31 ortholog.

    Evidence ChIP, RNAi knockdown, tandem affinity purification–mass spectrometry, and immunofluorescence in T. brucei and L. major

    PMID:39523652

    Open questions at the time
    • Degree to which parasite-specific interactors are functionally equivalent to human heterotrimer components is unknown
    • Cross-species complementation has not been attempted

Open questions

Synthesis pass · forward-looking unresolved questions
  • The mechanism by which POLR3C specifically contributes to cytosolic DNA sensing — whether via a moonlighting function or solely through its role in the Pol III heterotrimer — and the structural basis of disease-causing mutations' effects on initiation kinetics remain unresolved.
  • No separation-of-function mutants distinguish POLR3C's transcription-initiation role from its innate immunity role
  • No kinetic or single-molecule studies on heterotrimer–promoter engagement exist
  • The functional significance of the iron-sulfur cluster for initiation versus complex stability has not been dissected

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0005198 structural molecule activity 3 GO:0140223 general transcription initiation factor activity 2
Localization
GO:0005654 nucleoplasm 2 GO:0005634 nucleus 1
Pathway
R-HSA-74160 Gene expression (Transcription) 5 R-HSA-168256 Immune System 1
Partners
PKP2POLR3APOLR3DPOLR3F
Complex memberships
RNA Pol III holoenzymeRPC32/RPC39/RPC62 heterotrimer

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1997 Human RPC32 (POLR3C), RPC39, and RPC62 form a stable subcomplex that is specific to RNA Pol III. This subcomplex dissociates from the Pol III core under partial denaturing/high-salt conditions. The core lacking the subcomplex can perform elongation and termination on a tailed template but cannot perform promoter-dependent transcription initiation; specific initiation is restored by adding back the natural or recombinant RPC32/RPC39/RPC62 subcomplex. RPC39 within the subcomplex physically interacts with hTBP and hTFIIIB90, suggesting the subcomplex directs Pol III binding to the TFIIIB–DNA complex. Immunopurification, sucrose gradient sedimentation, reconstituted in vitro transcription assays with recombinant subcomplex, direct binding assays Genes & development High 9171375
1999 The TFIIIC90 subunit of human TFIIIC interacts directly with the RPC39 (POLR3D) and RPC62 (POLR3F) subunits of the Pol III initiation-specific subcomplex that contains POLR3C (RPC32), providing a physical link between TFIIIC and the Pol III holoenzyme during preinitiation complex assembly. Immunodepletion, immunoprecipitation, in vitro interaction assays Molecular and cellular biology Medium 10523658
2001 Plakophilin 2, a dual-location desmosomal/nuclear protein, is present in the Pol III holoenzyme but not the core complex, and it co-immunoselects with other Pol III subunits and TFIIIB. Because the holoenzyme but not the core contains the RPC32/RPC39/RPC62 subcomplex (which includes POLR3C), this association places plakophilin 2 in a nuclear particle containing the POLR3C-containing subcomplex. Co-immunoprecipitation, in vitro binding assay with RPC155, sucrose gradient co-sedimentation Proceedings of the National Academy of Sciences of the United States of America Medium 11416169
2015 Crystal structure of the human RPC62–RPC32β (POLR3F–POLR3C) complex was solved. RPC32β (POLR3C) uses a core-interacting domain to associate with the extended winged-helix 1 and 2 (eWH1/2) domains and the coiled-coil domain of RPC62. POLR3C acts as a molecular bridge between the RPC62 domains. Fitting the complex into Pol III EM density indicates that POLR3C has a bi-functional role: contacting the largest Pol III subunit and exposing solvent-facing residues for additional interactions. X-ray crystallography, fitting into EM density Journal of structural biology High 26394183
2017 Heterozygous missense mutations in POLR3C confer increased susceptibility to severe varicella zoster virus (VZV) infection. Leukocytes from a patient with a POLR3C mutation showed impaired IFN induction in response to synthetic DNA and VZV-derived DNA, defective IFN production upon VZV infection, and reduced control of VZV replication. These phenotypes were rescued by transduction with the wild-type POLR3C allele, establishing that POLR3C is required for the RNA Pol III-dependent DNA-sensing pathway that triggers innate IFN responses. Patient leukocyte functional assays (IFN induction, viral replication), lentiviral rescue with WT allele The Journal of clinical investigation High 28783042
2021 Cryo-EM structures of human RNA Pol III (2.8–3.3 Å) in unbound and transcribing states resolved the heterotrimer subcomplex containing POLR3C (RPC32). An iron-sulfur cluster was identified that tethers the heterotrimer subcomplex (including POLR3C) to the Pol III core, an element absent in yeast Pol III. The structures enabled mapping of disease-related mutations within POLR3C and the wider complex. Cryo-electron microscopy, structural modelling Nature structural & molecular biology High 33558764
2024 In trypanosomatid parasites (T. brucei and L. major), the C82 subunit (ortholog of human POLR3C) localizes to the nucleus, binds Pol III-dependent genes (tRNA, 5S rRNA loci), and forms a stable subcomplex with the C34 ortholog. Knock-down by RNAi significantly reduced tRNA and 5S rRNA levels and caused cell death in procyclic T. brucei. Tandem affinity purifications identified C34 and genus-specific putative regulators as interacting partners, but no C31 ortholog was detected, indicating divergence from the canonical three-subunit subcomplex. Chromatin immunoprecipitation, RNA interference knockdown, tandem affinity purification–mass spectrometry, immunofluorescence localization Parasitology Medium 39523652

Source papers

Stage 0 corpus · 60 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
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
2015 The BioPlex Network: A Systematic Exploration of the Human Interactome. Cell 1118 26186194
2017 Architecture of the human interactome defines protein communities and disease networks. Nature 1085 28514442
2015 A human interactome in three quantitative dimensions organized by stoichiometries and abundances. Cell 1015 26496610
2014 A proteome-scale map of the human interactome network. Cell 977 25416956
2020 A reference map of the human binary protein interactome. Nature 849 32296183
2009 RIG-I-dependent sensing of poly(dA:dT) through the induction of an RNA polymerase III-transcribed RNA intermediate. Nature immunology 712 19609254
2021 Dual proteome-scale networks reveal cell-specific remodeling of the human interactome. Cell 705 33961781
2012 A census of human soluble protein complexes. Cell 689 22939629
2011 Phylogenetic-based propagation of functional annotations within the Gene Ontology consortium. Briefings in bioinformatics 656 21873635
1994 Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides. Gene 492 8125298
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
2005 Diversification of transcriptional modulation: large-scale identification and characterization of putative alternative promoters of human genes. Genome research 409 16344560
2015 Panorama of ancient metazoan macromolecular complexes. Nature 407 26344197
2007 Systematic analysis of the protein interaction network for the human transcription machinery reveals the identity of the 7SK capping enzyme. Molecular cell 367 17643375
2021 A proximity-dependent biotinylation map of a human cell. Nature 339 34079125
2018 An AP-MS- and BioID-compatible MAC-tag enables comprehensive mapping of protein interactions and subcellular localizations. Nature communications 201 29568061
2020 Synthetic Lethal and Resistance Interactions with BET Bromodomain Inhibitors in Triple-Negative Breast Cancer. Molecular cell 159 32416067
2018 MYC Protein Interactome Profiling Reveals Functionally Distinct Regions that Cooperate to Drive Tumorigenesis. Molecular cell 152 30415952
2009 The effect of Gd@C82(OH)22 nanoparticles on the release of Th1/Th2 cytokines and induction of TNF-alpha mediated cellular immunity. Biomaterials 151 19403166
2012 Molecular mechanism of pancreatic tumor metastasis inhibition by Gd@C82(OH)22 and its implication for de novo design of nanomedicine. Proceedings of the National Academy of Sciences of the United States of America 143 22949663
2018 Interactome Rewiring Following Pharmacological Targeting of BET Bromodomains. Molecular cell 136 30554943
1997 Three human RNA polymerase III-specific subunits form a subcomplex with a selective function in specific transcription initiation. Genes & development 132 9171375
2011 Interactions of pathological hallmark proteins: tubulin polymerization promoting protein/p25, beta-amyloid, and alpha-synuclein. The Journal of biological chemistry 131 21832049
2017 Inborn errors in RNA polymerase III underlie severe varicella zoster virus infections. The Journal of clinical investigation 126 28783042
2007 Toward a confocal subcellular atlas of the human proteome. Molecular & cellular proteomics : MCP 114 18029348
2006 Antioxidative function and biodistribution of [Gd@C82(OH)22]n nanoparticles in tumor-bearing mice. Biochemical pharmacology 113 16436273
2018 Histone Interaction Landscapes Visualized by Crosslinking Mass Spectrometry in Intact Cell Nuclei. Molecular & cellular proteomics : MCP 101 30021884
2001 Nuclear particles containing RNA polymerase III complexes associated with the junctional plaque protein plakophilin 2. Proceedings of the National Academy of Sciences of the United States of America 98 11416169
1999 The TFIIIC90 subunit of TFIIIC interacts with multiple components of the RNA polymerase III machinery and contains a histone-specific acetyltransferase activity. Molecular and cellular biology 86 10523658
2021 Cryo-EM structures of human RNA polymerase III in its unbound and transcribing states. Nature structural & molecular biology 80 33558764
2007 Bacteriochlorophyllide c C-8(2) and C-12(1) methyltransferases are essential for adaptation to low light in Chlorobaculum tepidum. Journal of bacteriology 79 17586634
2022 SARS-CoV-2 N Protein Antagonizes Stress Granule Assembly and IFN Production by Interacting with G3BPs to Facilitate Viral Replication. Journal of virology 75 35652658
2017 Inhibition of β-Catenin Signaling in the Skin Rescues Cutaneous Adipogenesis in Systemic Sclerosis: A Randomized, Double-Blind, Placebo-Controlled Trial of C-82. The Journal of investigative dermatology 45 28807667
2011 Biosafety assessment of Gd@C82(OH)22 nanoparticles on Caenorhabditis elegans. Nanoscale 32 21541378
2015 Quantitative analysis of Gd@C82(OH)22 and cisplatin uptake in single cells by inductively coupled plasma mass spectrometry. Analytical and bioanalytical chemistry 31 25701412
2019 β-catenin signaling inhibitors ICG-001 and C-82 improve fibrosis in preclinical models of endometriosis. Scientific reports 25 31882904
2024 Rational Design of Dual-Functionalized Gd@C82 Nanoparticles to Relieve Neuronal Cytotoxicity in Alzheimer's Disease via Inhibition of Aβ Aggregation. ACS nano 17 38840269
2015 DNA polymerases κ and ζ cooperatively perform mutagenic translesion synthesis of the C8-2'-deoxyguanosine adduct of the dietary mutagen IQ in human cells. Nucleic acids research 13 26220181
2014 Induction of apoptosis through ER stress and TP53 in MCF-7 cells by the nanoparticle [Gd@C82(OH)22]n: A systems biology study. Methods (San Diego, Calif.) 13 24440483
2014 Gd@C82(OH)22 nanoparticles constrain macrophages migration into tumor tissue to prevent metastasis. Journal of nanoscience and nanotechnology 13 24738346
2013 Metallofullerenol Gd@C₈₂(OH)₂₂ distracts the proline-rich-motif from putative binding on the SH3 domain. Nanoscale 13 23423582
2015 Structural analysis of human RPC32β-RPC62 complex. Journal of structural biology 11 26394183
2001 The C(8)-(2'-deoxy-beta-D-ribofuranoside) of 7-deazaguanine: synthesis and base pairing of oligonucleotides with unusually linked nucleobases. The Journal of organic chemistry 10 11348111
2021 Effects of Aqueous Dispersions of C60, C70 and Gd@C82 Fullerenes on Genes Involved in Oxidative Stress and Anti-Inflammatory Pathways. International journal of molecular sciences 8 34200169
2010 The C8-2'-deoxyguanosine adduct of 2-amino-3-methylimidazo[1,2-d]naphthalene, a carbocyclic analogue of the potent mutagen 2-amino-3-methylimidazo[4,5-f]quinoline, is a block to replication in vitro. Chemical research in toxicology 8 20377178
2018 Distance Measurement of a Noncovalently Bound Y@C82 Pair with Double Electron Electron Resonance Spectroscopy. Journal of the American Chemical Society 7 29860839
2011 An anti-tumor nanoparticle, [Gd@C82(OH)22]n, induces macrophage activation. Journal of nanoscience and nanotechnology 6 21449388
2010 Transmembrane delivery of aggregated [Gd@C82(OH)22]n nanoparticles. Journal of nanoscience and nanotechnology 6 21121366
2014 Unprecedented chemical reactivity of a paramagnetic endohedral metallofullerene La@C(s)-C82 that leads hydrogen addition in the 1,3-dipolar cycloaddition reaction. Journal of the American Chemical Society 3 25469552
2023 Effects of Aqueous Dispersions of C60, C70, and Gd@C82 Fullerenes on DNA Oxidative Damage/Repair and Apoptosis in Human Embryonic Lung Fibroblasts. ACS biomaterials science & engineering 2 36821424
2020 6-Nitrochrysene-Derived C8-2'-Deoxyadenosine Adduct: Synthesis of Site-Specific Oligodeoxynucleotides and Mutagenicity in Escherichia coli. Chemical research in toxicology 2 31903755
2007 Calculations of the C2 fragmentation energies of higher fullerenes C80 and C82. Journal of molecular modeling 2 17588181
2024 Computational insights into Diels-Alder reactions of paramagnetic endohedral metallofullerenes: M@C82 (M = Sc, Y, La) and La@C72. Physical chemistry chemical physics : PCCP 1 39377172
2017 Synthesis of Oligodeoxynucleotides Containing a C8-2'-Deoxyguanosine Adduct Formed by the Carcinogen 3-Nitrobenzanthrone. Current protocols in nucleic acid chemistry 1 28628210
2026 Water-soluble gadolinium fullerenes Gd@C82-TEGs as a potential magnetic resonance imaging contrast agent. PloS one 0 41961832
2025 Noncovalent interactions and properties of host-guest systems based on C82/C82Gd bucky-balls and symmetry broken nanohoop TP-[11]CPP. The Journal of chemical physics 0 40035581
2025 Venetoclax synergizes with Wnt/β-catenin inhibitor C-82 in acute myeloid leukemia by increasing the degradation of Mcl-1 protein. Cancer cell international 0 40442688
2024 Analyses of the essential C82 subunit uncovered some differences in RNA polymerase III transcription between Trypanosoma brucei and Leishmania major. Parasitology 0 39523652