RNA polymerase III
Transcription in eukaryotic cells involves 3 distinct RNA polymerases, RNA polymerase I (pol I), RNA polymerase II (pol II), and RNA polymerase III (pol III).
Pol III transcribes significantly shorter genes than those transcribed by pol I and pol II.
RNA polymerase III is a porteic complex with sereral subunits, as POLR3K (MIM.606007).
In the absence of proteins such as TFIIS (TCEA1) (MIM.601425) and TFIIF (GTF2F1) (MIM.189968), RNA polymerases are prevented from completing transcription, a phenomenon known as transcription arrest.
The role of RNA polymerase (Pol) III in eukaryotic transcription is commonly thought of as being restricted to a small set of highly expressed, housekeeping non-protein-coding (nc)RNA genes.
Recent studies have remarkably expanded the set of known Pol III-synthesized ncRNAs, suggesting that gene-specific Pol III regulation is more common than previously appreciated.
Newly identified Pol III transcripts include small nucleolar RNAs, microRNAs, short interspersed nuclear element-encoded or tRNA-derived RNAs and novel classes of ncRNA that can display significant sequence complementarity to protein-coding genes and might thus regulate their expression.
References
Dieci G, Fiorino G, Castelnuovo M, Teichmann M, Pagano A. The expanding RNA polymerase III transcriptome. Trends Genet. 2007 Dec;23(12):614-22. PMID: 17977614