COMPLEX INTERACTIONS BETWEEN YEAST TFIIIB AND TFIIIC

Transcription of yeast class III genes requires the sequential assembl y of the general transcription factors TFIIIC and TFIIIB, and of RNA p olymerase III, into an initiation complex composed of at least 25 poly peptides. The 70-kDa subunit of TFIIIB (TFIIIB70) is central in this n etwork of interactions as it contacts both TATA-binding protein and a subunit of polymerase III. We show here that the TATA-binding protein interacts with the carboxyl-terminal part of TFIIIB70. TFIIIB70 also c ontacts TFIIIC (factor tau) via its tau 131 subunit. The protein domai ns of tau 131 and TFIIB70 involved in this interaction, either positiv ely or negatively, were mapped using the two-hybrid system. We provide evidence that intramolecular interactions mask functional domains in both polypeptides.