Affinage

POLR1C

DNA-directed RNA polymerases I and III subunit RPAC1 · UniProt O15160

Length
346 aa
Mass
39.2 kDa
Annotated
2026-06-10
14 papers in source corpus 7 papers cited in narrative 7 extracted findings
Cross-family judge vs UniProt: Affinage preferred faithfulness: 4/4 claims corpus-supported (100%)

Mechanistic narrative

Synthesis pass · prose summary of the discoveries below

POLR1C (RPA40/RPC40) is a core subunit shared between RNA polymerase I and III, originally identified by purification of the eleven-subunit RNA polymerase I and shown by sequence analysis to be the homolog of yeast RPC40 and a relative of bacterial alpha-subunit-type core subunits (PMID:7929437). Because it serves two polymerases, distinct disease mutations have separable molecular consequences: leukodystrophy-associated recessive mutations selectively impair assembly and nuclear import of RNA polymerase III—without affecting RNA polymerase I—thereby reducing POLR3 binding to its target genes, whereas Treacher Collins syndrome (TCS) mutations in the same gene do not produce this selective POLR3 defect (PMID:26151409). Other TCS3-associated missense mutations (R279Q, R279W) mislocalize POLR1C from the nucleus to the lysosome, reduce phosphorylation of the mTOR targets 4E-BP1 and S6, and block chondrogenic differentiation, while biallelic variants additionally drive aberrant intron retention in POLR1C transcripts as a downstream pathomechanism (PMID:29567474, PMID:33134519). In vivo, loss of polr1c in zebrafish causes deficient ribosome biogenesis and Tp53-dependent neuroepithelial apoptosis that depletes migrating neural crest cells, producing craniofacial skeletal anomalies; genetic inhibition of tp53 suppresses this cell death and ameliorates the skeletal defects, placing POLR1C upstream of p53-dependent apoptosis within a defined early embryonic window of craniofacial development (PMID:27448281, PMID:26972049, PMID:29128566). POLR1C mutations thus cause both a leukodystrophy (via selective POLR3 dysfunction) and Treacher Collins syndrome.

Mechanistic history

Synthesis pass · year-by-year structured walk · 6 steps
  1. 1994 Medium

    Established the identity of POLR1C as a shared core subunit of the nuclear RNA polymerases, answering what protein it is and how it relates to known polymerase machinery.

    Evidence Protein purification of RNA polymerase I to homogeneity, cDNA cloning, and sequence comparison in mouse

    PMID:7929437

    Open questions at the time
    • Did not resolve which polymerase functions depend differentially on this subunit
    • No structural placement within the assembled enzymes
  2. 2015 High

    Resolved how mutations in a subunit shared by two polymerases can cause distinct diseases, showing leukodystrophy mutations selectively cripple POLR3 assembly, import, and target binding while sparing POLR1.

    Evidence Shotgun proteomics, ChIP-seq, and nuclear fractionation comparing mutation classes

    PMID:26151409

    Open questions at the time
    • Mechanism by which specific residues bias toward POLR3 versus POLR1 assembly not defined
    • Does not explain the TCS phenotype molecularly
  3. 2016 High

    Defined the in vivo developmental consequence of POLR1C loss, placing it upstream of Tp53-dependent neural crest apoptosis driving craniofacial malformation.

    Evidence Zebrafish loss-of-function mutants, morpholino/CRISPR, and tp53 genetic epistasis with histology/imaging

    PMID:26972049 PMID:27448281

    Open questions at the time
    • Link between ribosome biogenesis deficit and p53 activation not mechanistically dissected
    • Cell-type specificity of neural crest vulnerability unexplained
  4. 2017 Medium

    Established a critical early embryonic time window for POLR1C in craniofacial development by temporally restricting rescue.

    Evidence Photo-morpholino temporal rescue in zebrafish with neural crest imaging, apoptosis, and p53 mRNA readouts

    PMID:29128566

    Open questions at the time
    • Molecular basis of the temporal sensitivity unknown
    • Single-lab temporal rescue paradigm
  5. 2018 Medium

    Revealed an additional pathomechanism for TCS3 mutations distinct from polymerase assembly: mislocalization to the lysosome with suppression of mTOR signaling and chondrogenesis.

    Evidence Immunofluorescence/fractionation, phospho-western for 4E-BP1 and S6, and chondrogenic differentiation assay in ATDC5 cells expressing R279Q/R279W

    PMID:29567474

    Open questions at the time
    • How nuclear protein is rerouted to lysosome unresolved
    • Direct connection between POLR1C and mTOR pathway not established
    • Single cell-line study
  6. 2020 Medium

    Identified aberrant splicing of POLR1C itself as a downstream consequence of biallelic variants, expanding the mutational pathomechanism beyond protein mislocalization.

    Evidence Exome analysis, long-read sequencing for splice quantification, expression and localization studies in patient cells

    PMID:33134519

    Open questions at the time
    • Whether intron retention extends to other POLR1/POLR3 target genes untested
    • Causal contribution of splicing defect to phenotype not isolated

Open questions

Synthesis pass · forward-looking unresolved questions
  • How distinct POLR1C mutations partition into leukodystrophy versus Treacher Collins outcomes at the structural and assembly level remains unresolved.
  • No structural model linking mutated residues to selective POLR1 vs POLR3 effects
  • Unifying mechanism connecting ribosome biogenesis, p53 apoptosis, and mTOR signaling absent

Mechanism profile

Synthesis pass · controlled-vocabulary classification · explore literature graph →
Molecular activity
GO:0140098 catalytic activity, acting on RNA 2
Localization
GO:0005634 nucleus 2 GO:0005764 lysosome 1
Pathway
R-HSA-1266738 Developmental Biology 2 R-HSA-74160 Gene expression (Transcription) 2
Complex memberships
RNA polymerase IRNA polymerase III

Evidence

Reading pass · 7 per-paper findings extracted from the source corpus
Year Finding Method Journal Conf PMIDs
1994 Mouse RPA40 (POLR1C) was identified as a subunit of RNA polymerase I, purified to homogeneity with 11 subunits; protein sequence analysis showed it is the homolog of yeast RPC40, sharing homology with the alpha subunit of E. coli RNA polymerase, yeast RPB3, and human RPB33, establishing it as a core subunit shared across RNA polymerases. Protein purification, cDNA cloning, protein sequence analysis The Journal of biological chemistry Medium 7929437
2015 Recessive mutations in POLR1C that cause leukodystrophy (but not Treacher Collins syndrome mutations in the same gene) selectively impair assembly and nuclear import of RNA polymerase III (POLR3) but not RNA polymerase I (POLR1), leading to decreased POLR3 binding to its target genes. This demonstrates that distinct mutations in a shared subunit can selectively affect one of the two polymerases it serves. Shotgun proteomics (to assess polymerase assembly), ChIP sequencing (to assess POLR3 target gene binding), nuclear fractionation (to assess nuclear import) Nature communications High 26151409
2016 Loss-of-function of polr1c in zebrafish results in deficient ribosome biogenesis, Tp53-dependent neuroepithelial cell death, and a deficiency of migrating neural crest cells leading to craniofacial skeletal anomalies; genetic inhibition of tp53 suppresses neuroepithelial cell death and ameliorates skeletal defects, placing polr1c upstream of tp53-dependent apoptosis in neural crest development. Zebrafish homozygous mutant analysis, genetic epistasis (tp53 mutant suppressor), histology/imaging of neural crest cells and cartilage PLoS genetics High 26972049 27448281
2016 Knockdown or knockout of polr1c in zebrafish causes mis-expression of neural crest cells during early development leading to TCS phenotype; the TCS facial phenotype is partially rescued in a p53 mutant background, placing POLR1C function upstream of the p53 pathway in neural crest cell fate. Zebrafish morpholino knockdown and CRISPR knockout, p53 mutant genetic rescue, next-generation sequencing/bioinformatics of mutant transcriptomes Biochimica et biophysica acta Medium 26972049
2017 Restoration of polr1c expression specifically at 8 hours post-fertilization (but not after 30 hours) rescues the TCS facial malformation phenotype in zebrafish by correcting neural crest cell expression, reducing cell death, and normalizing p53 mRNA levels, defining a critical early embryonic time window for POLR1C function in craniofacial development. Photo-morpholino temporal rescue experiment in zebrafish, neural crest cell imaging, p53 mRNA quantification The American journal of pathology Medium 29128566
2018 TCS3-associated missense mutations R279Q and R279W in POLR1C cause aberrant intracellular localization of the protein from the nucleus to the lysosome, decrease phosphorylation of mTOR signaling targets 4E-BP1 and ribosomal S6 proteins, and inhibit chondrogenic differentiation in mouse ATDC5 cells. Subcellular localization by immunofluorescence/fractionation, phosphorylation assay by western blot, chondrogenic differentiation assay in ATDC5 cells expressing mutant POLR1C Biochemical and biophysical research communications Medium 29567474
2020 Biallelic POLR1C variants (M56K and I199F) cause altered protein subcellular localization, decreased protein expression, and trigger abnormal inclusion of introns in 85% of POLR1C transcripts in patient cells; each heterozygous variant also caused intron inclusion on both mutant and wild-type alleles, suggesting POLR1C variants dysregulate splicing of POLR1C itself and potentially other target genes as a downstream pathomechanism. Exome analysis, cell expression studies, long-read sequencing for splice analysis, allelic segregation analysis in carrier parents Neurology. Genetics Medium 33134519

Source papers

Stage 0 corpus · 14 papers · ranked by NIH iCite citations
Year Title Journal Citations PMID
2015 Recessive mutations in POLR1C cause a leukodystrophy by impairing biogenesis of RNA polymerase III. Nature communications 145 26151409
2016 The Roles of RNA Polymerase I and III Subunits Polr1c and Polr1d in Craniofacial Development and in Zebrafish Models of Treacher Collins Syndrome. PLoS genetics 88 27448281
2016 Pathogenesis of POLR1C-dependent Type 3 Treacher Collins Syndrome revealed by a zebrafish model. Biochimica et biophysica acta 43 26972049
2019 Clinical spectrum of POLR3-related leukodystrophy caused by biallelic POLR1C pathogenic variants. Neurology. Genetics 42 32042905
1994 High conservation of subunit composition of RNA polymerase I(A) between yeast and mouse and the molecular cloning of mouse RNA polymerase I 40-kDa subunit RPA40. The Journal of biological chemistry 36 7929437
2019 Novel POLR1C mutation in RNA polymerase III-related leukodystrophy with severe myoclonus and dystonia. Molecular genetics & genomic medicine 12 31368241
2023 Genome-Based Analysis of the Potential Bioactivity of the Terrestrial Streptomyces vinaceusdrappus Strain AC-40. Biology 10 36979037
2023 Craniofacial features of POLR3-related leukodystrophy caused by biallelic variants in POLR3A, POLR3B and POLR1C. Journal of medical genetics 9 37197783
2020 Molecular imprints of plant beneficial Streptomyces sp. AC30 and AC40 reveal differential capabilities and strategies to counter environmental stresses. Microbiological research 8 32114361
2007 Nucleotide and deduced amino acid sequences of a subtilisin-like serine protease from a deep-sea bacterium, Alkalimonas collagenimarina AC40(T). Applied microbiology and biotechnology 8 17786425
2020 POLR1C variants dysregulate splicing and cause hypomyelinating leukodystrophy. Neurology. Genetics 5 33134519
2017 Restoration of polr1c in Early Embryogenesis Rescues the Type 3 Treacher Collins Syndrome Facial Malformation Phenotype in Zebrafish. The American journal of pathology 5 29128566
2018 Treacher Collins syndrome 3 (TCS3)-associated POLR1C mutants are localized in the lysosome and inhibits chondrogenic differentiation. Biochemical and biophysical research communications 3 29567474
2022 Next-Generation Sequencing Reveals Novel Homozygous Missense Variant c.934T > C in POLR1C Gene Causing Leukodystrophy and Hypomyelinating Disease. Frontiers in pediatrics 2 35685919

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