| Health / Medical Topics |
RNA Polymerase III Transcription Pathway
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 are 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. (NCI Thesaurus/BIOCARTA)
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