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POLR1C
RNA polymerase I and III subunit C
POLR1C is located on the short (p) arm of chromosome 6, at band 6p21.1. Arm ratio per GRCh38 - banding schematic.
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Overview
POLR1C encodes a 346-amino-acid protein that functions as a shared subunit of RNA polymerase I and RNA polymerase III. These two enzymes play central roles in transcribing ribosomal RNA genes and other non-coding RNA genes, processes that underpin protein synthesis and cellular function. Research indicates that POLR1C is particularly important during embryonic development, when rapidly dividing cells require high levels of ribosome production.
Variants in POLR1C are associated with a spectrum of developmental disorders, most notably Treacher Collins syndrome, a condition characterised by underdevelopment of facial bones and tissues. The gene is also linked to neurodevelopmental phenotypes and skeletal abnormalities. Understanding POLR1C function helps explain how disruptions to fundamental cellular machinery can manifest as tissue-specific developmental defects.
What the gene does
The POLR1C protein serves as a structural and catalytic component of both RNA polymerase I and RNA polymerase III. RNA polymerase I is dedicated to transcribing ribosomal RNA genes, which produce the RNA scaffolds that form ribosomes - the cellular machines responsible for translating messenger RNA into proteins. RNA polymerase III transcribes transfer RNA genes, 5S ribosomal RNA, and other small RNAs involved in protein synthesis and RNA processing.
By participating in both polymerase complexes, POLR1C helps coordinate the production of complementary components required for efficient translation. The protein contributes to enzyme assembly and likely plays a role in positioning the polymerase machinery correctly on gene promoters. Evidence suggests that POLR1C function is especially critical in tissues undergoing rapid growth and differentiation, such as the developing craniofacial skeleton, where high rates of protein synthesis are necessary to support morphogenesis. Reduced polymerase activity resulting from POLR1C deficiency leads to decreased ribosomal RNA production, triggering cellular stress responses that can cause selective tissue abnormalities during development.
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Chromosome location
POLR1C is located on the short arm of chromosome 6 at position p21.1. This chromosomal region contains numerous genes involved in immune function and development. The gene spans approximately 15 kilobases of genomic DNA and comprises multiple exons that encode the 346-amino-acid protein.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The POLR1C protein is relatively compact at 346 amino acids and functions primarily through its integration into the larger polymerase complexes, where it interacts with other subunits to form the functional transcription machinery.
Key variants
Pathogenic variants in POLR1C include missense changes, small deletions, and splice-site alterations that reduce the stability or activity of the encoded protein. At least six different variants have been documented in individuals with Treacher Collins syndrome, and additional variants have been identified in patients with broader developmental presentations. Most disease-causing changes appear to impair the assembly or catalytic efficiency of RNA polymerase complexes, leading to reduced ribosomal RNA synthesis during critical developmental windows.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in POLR1C are primarily associated with Treacher Collins syndrome, a condition affecting craniofacial development that typically presents with underdeveloped cheekbones, jaw abnormalities, and outer-ear malformations. Some affected individuals also experience hearing loss and cleft palate. Beyond classic Treacher Collins syndrome, POLR1C variants have been linked to presentations including intellectual disability, white matter abnormalities on brain imaging, and skeletal dysplasia. The range of phenotypes reflects the fundamental importance of ribosomal RNA production across multiple developmental programmes, with the most rapidly proliferating tissues often showing the greatest sensitivity to POLR1C dysfunction.
No disease links recorded for this gene in our reference set.
UK clinical status
POLR1C appears on multiple NHS Genomic Medicine Service gene panels with green classification, indicating strong evidence for clinical validity. The gene is included in the Clefting panel, DDG2P (Developmental Disorders Genotype-to-Phenotype database), Deafness and Congenital Structural Abnormalities panel, Fetal Anomalies panel, Inherited White Matter Disorders panel, Intellectual Disability panel, Skeletal Dysplasia panel, and the White Matter Disorders and Cerebral Calcification narrow panel. This broad representation reflects the diverse clinical presentations associated with POLR1C variants and ensures that testing is available through NHS pathways for patients presenting with relevant developmental features.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the difference between RNA polymerase I and RNA polymerase III?
RNA polymerase I specialises in transcribing ribosomal RNA genes that produce the large RNA molecules forming the core of ribosomes. RNA polymerase III transcribes transfer RNA genes and other small RNAs, including 5S ribosomal RNA. POLR1C functions as a shared subunit in both enzymes, coordinating their activities to support efficient protein synthesis.
Why does POLR1C dysfunction primarily affect craniofacial development?
Craniofacial tissues undergo particularly rapid cell division and differentiation during embryonic development, requiring very high rates of ribosome production to support protein synthesis. Reduced RNA polymerase activity caused by POLR1C variants may be better tolerated in slower-growing tissues but triggers developmental abnormalities in regions with the highest biosynthetic demands, such as the developing facial bones.
Is POLR1C testing available through the NHS?
Yes, POLR1C is included on multiple NHS Genomic Medicine Service gene panels with green classification, meaning testing is available for patients whose clinical presentation matches the relevant panel criteria, such as craniofacial abnormalities, hearing loss, intellectual disability, or white matter disorders. A healthcare provider can arrange appropriate genetic testing through NHS pathways.