RNA polymerase III transcription
Unlike the RNA polymerase II that transcribes a large variety of genes that encode proteins, RNA polymerase III transcribes only a limited number of genes (i.e., 5S rRNA. tRNA. 7SL RNA, U6 snRNA and a few other small stable RNAs); however, the transcriptional activities of RNA pol III along with pol I account for 80% of total RNA synthesis. The A and B block sequences found in most pol III promoters is recognized by a multisubunit complex, TFIIIC. The binding of TFIIIC recruits TFIIIB, a complex of polypeptides (in human, TATA-binding protein (TBP), TFIIB-related factor (BRF), and one or more unidentified protein). Once TFIIIB is brought to the general location by TFIIIC and optimally positioned by TBP, the transcription initiates about 30bp downstream. The transcription process requires the melting of dsDNA and participation of TFIIIB. Unlike pol I and II, pol III termination occurs efficiently at four or more T residues without other protein factors. La protein can stimulate the release of RNA and pol III transcription; however, deletion of La has no apparent effect on pol III activity.
Contributor: Joseph Chuang, PhD
REFERENCES: Huang Y, Maraia RJ. Comparison of the RNA polymerase III transcription machinery in Schizosaccharomyces pombe, Saccharomyces cerevisiae and human. Nucleic Acids Res. 2001 Jul 1;29(13):2675-90. Review. Kassavetis GA et al. The RNA polymerase III transcription initiation factor TFIIIB participates in two steps of promoter opening. EMBO J. 2001 Jun 1;20(11):2823-34 Paule M.R., White R.J. Transcription by RNA polymerase I and III. Nucleic Acids Res. 2000; 28 (6):1283-1298.
