THE ROLE OF THE TATA-BINDING PROTEIN IN THE ASSEMBLY AND FUNCTION OF THE MULTISUBUNIT YEAST RNA POLYMERASE-III TRANSCRIPTION FACTOR, TFIIIB

The Saccharomyces cerevisiae RNA polymerase III transcription factor (TF)IIIB has been assembled from three components. An assembly pathway of these polypeptides, which specifies their interactions, has been determined. The TATA-binding protein, TBP, and the TFIIB-related BRF1 gene product BRF, together reconstitute the transcription factor activity and TFIIIC-dependent DNA-binding activity of the B' component of TFIIIB. BRF alone weakly binds to a TFIIIC-tRNA gene complex; TBP greatly stabilizes this interaction. B" transcription factor actitivity is recovered with its previously identified 90 kd polypeptide from SDS-polyacrylamide gels. Incorporation of the 90 kd B" protein into the transcription complex requires TBP. The heparin-resistant TFIIIB-DNA complex retains all three of its constituent proteins, TBP, BRF, and B".