POLR3A encodes the catalytic core subunit of RNA polymerase III (Pol III), a DNA-dependent RNA polymerase that synthesizes small non-coding RNAs including 5S rRNA, tRNAs, snRNAs, and miRNAs from over 500 genomic loci 1. POLR3A forms the active catalytic center with subunit POLR3B, with the POLR3A-contributed DxDGD motif coordinating magnesium ions essential for phosphodiester bond formation during nucleotide addition 2. The Pol III transcription cycle proceeds through initiation, elongation, and termination stages, with POLR3A recruited to type I, II, or III promoters via general transcription factors 3. Beyond transcription, POLR3A functions as a nuclear and cytosolic DNA sensor in innate immunity, detecting non-self dsDNA and transcribing it into dsRNA that triggers type I interferon responses through the RIG-I pathway 4. Additionally, POLR3A is actively recruited to DNA double-strand breaks by the MRN complex to synthesize protective RNA-DNA hybrids during homologous recombination repair 5. Clinically, POLR3A mutations cause hypomyelinating leukodystrophy type 7 and account for approximately 3% of autosomal recessive spastic ataxia cases, particularly when intronic mutations activate cryptic splice sites, presenting with adolescent-onset progressive spastic ataxia, tremor, and dental abnormalities 6. POLR3A mutations also associate with varicella zoster virus susceptibility 4, and somatic POLR3A mutations in cancer patients coincide with POLR3-directed autoimmunity in scleroderma 7.