POLR3B
RNA Polymerase III Subunit B
Gene Information Card
| Symbol | POLR3B |
|---|---|
| Full Name | RNA Polymerase III Subunit B |
| Gene Type | Protein coding |
| Chromosomal Location | 12q23.3 |
| NCBI Gene ID | 55703 ncbi.nlm.nih.gov/gene/55703 |
| Ensembl ID | ENSG00000111206 |
| UniProt ID | Q9NW08 |
| OMIM ID | 614366 |
| HGNC ID | 30348 |
| Aliases | RPC2, RPC155, POLR3B1, HLD8 |
Description
POLR3B encodes the second largest subunit of RNA polymerase III, which transcribes small non-coding RNAs such as tRNAs, 5S rRNA, and U6 snRNA. This subunit is essential for polymerase assembly and catalytic activity. Mutations in POLR3B cause hypomyelinating leukodystrophy type 8 (HLD8) and other POLR3-related disorders, characterized by neurological deficits and abnormal myelination.
Disease Associations
| Disease category | Pathophysiological mechanism | Genomic evidence |
|---|---|---|
| Hypomyelinating leukodystrophy 8 (HLD8) | Loss-of-function mutations impair RNA polymerase III activity, reducing transcription of small RNAs needed for oligodendrocyte development and myelin maintenance. | ClinVar, OMIM |
| 4H syndrome (Hypomyelination, Hypodontia, Hypogonadotropic Hypogonadism) | Biallelic POLR3B mutations disrupt RNA Pol III function, leading to a spectrum of neurological and endocrine abnormalities. | OMIM, PubMed |
| POLR3-related leukodystrophy | Defective transcription of tRNAs and other Pol III targets affects protein synthesis in glial cells, causing progressive white matter disease. | ClinVar, NCBI |
Expression Profile
Tissue Expression
| Tissue | nTPM | level |
|---|---|---|
| Brain | 8.2 | Medium |
| Testis | 6.5 | Medium |
| Lung | 5.1 | Low |
| Liver | 4.3 | Low |
| Heart | 3.9 | Low |
Cell Line Expression
| Cell Line | nTPM | Notes |
|---|---|---|
| SH-SY5Y (neuroblastoma) | 9.8 | Neuronal model |
| HeLa (cervical carcinoma) | 7.4 | Epithelial |
| HEK293 (embryonic kidney) | 6.2 | Common cell line |
| K562 (leukemia) | 5.5 | Myeloid |
Data source：Human Protein Atlas（proteinatlas.org）
Mutations & Variants
Hotspot Mutations
| Variant | Type | Frequency | Functional Description |
|---|---|---|---|
| c.1567C>T (p.Arg523Trp) | Missense | Rare | Reduced Pol III activity; associated with HLD8 |
| c.308G>A (p.Arg103His) | Missense | Rare | Impaired subunit assembly; linked to 4H syndrome |
| c.1A>G (p.Met1?) | Start loss | Very rare | Complete loss of protein; severe phenotype |
Mutation functional classification
Loss of Function (LOF)
Most POLR3B mutations are loss-of-function, reducing RNA polymerase III activity and transcription of small non-coding RNAs.
Gain of Function (GOF)
No gain-of-function mutations reported.
Dominant Negative (DN)
Some missense mutations may exert dominant-negative effects by disrupting polymerase complex assembly, though evidence is limited.
View complete mutation data：
Gene Ontology (GO)
| • DNA-directed 5'-3' RNA polymerase activity (GO:0003899) | • RNA polymerase III activity (GO:0001056) |
| • Nucleus (GO:0005634) | • Transcription of RNA polymerase III (GO:0006383) |
| • tRNA transcription (GO:0042797) |
Pathways
• RNA polymerase III transcription (Reactome R-HSA-73779)
• Transcription of tRNA (Reactome R-HSA-74160)
• RNA polymerase III chain elongation (Reactome R-HSA-73854)
Protein Summary
POLR3B (RPC2) is a 155 kDa subunit of RNA polymerase III, forming part of the active center. It interacts with other subunits to catalyze DNA-directed RNA synthesis. The protein contains a conserved RNA polymerase domain and is essential for Pol III complex stability and function.
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