Core component of RNA polymerase III (Pol III) which synthesizes small non-coding RNAs using the four ribonucleoside triphosphates as substrates (PubMed:20413673, PubMed:30584594, PubMed:33335104, PubMed:33558764, PubMed:33558766, PubMed:33674783, PubMed:34675218). Can mediate Pol I proofreading of the nascent RNA transcript. Anchors into the Pol III active site to constantly monitor transcription fidelity, cleaves mis-incorporated 5'-ribonucleotides and restarts the transcription process. Once Pol III reaches the poly(dT) termination signal, can induce Pol III clamp opening and transcription termination (By similarity) (PubMed:33335104, PubMed:33558764, PubMed:33558766, PubMed:33674783, PubMed:34675218). Pol III plays an important role in sensing and limiting infection by intracellular bacteria and DNA viruses. Acts as a nuclear and cytosolic DNA sensor involved in innate immune response. Can sense non-self dsDNA that serves as template for transcription into dsRNA. The non-self RNA polymerase III transcripts, such as Epstein-Barr virus-encoded RNAs (EBERs) induce type I interferon and NF-kappa-B through the RIG-I pathway (PubMed:19609254, PubMed:19631370). {ECO:0000250|UniProtKB:Q04307, ECO:0000269|PubMed:19609254, ECO:0000269|PubMed:19631370, ECO:0000269|PubMed:20413673, ECO:0000269|PubMed:30584594, ECO:0000269|PubMed:33335104, ECO:0000269|PubMed:33558764, ECO:0000269|PubMed:33558766, ECO:0000269|PubMed:33674783, ECO:0000269|PubMed:34675218}. This is the function of POLR3K (RNA polymerase III subunit K, Ensembl gene identifier ENSG00000161980).