A subunit of yeast TFIIIC participates in the recruitment of TATA-binding protein

TFIIIC plays a key role in nucleating the assembly of the initiation factor TFIIIB on class III genes. We have characterized an essential gene, TFC8, encoding the 60-kDa polypeptide, tau 60, present in affinity-purified TFIII C. Hemagglutinin-tagged variants of tau 60 were found to be part of TFIIIC- tDNA complexes and to reside at least in part in the downstream DNA-binding domain tau B. Unexpectedly, the thermosensitive phenotype of N-terminally tagged tau 60 was suppressed by overexpression of tau 95, which belongs to the tau A domain, and by two TFIIIB components, TATA-binding protein (TBP) and B"/TFIIIB90 (but not by TFIIIB70). Mutant TFIIIC was deficient in the a ctivation of certain tRNA genes in vitro, and the transcription defect was selectively alleviated by increasing TBP concentration. Coimmunoprecipitati on experiments support a direct interaction between TBP and tau 60. It is s uggested that tau 60 links tau A and tau B domains and participates in TFII IB assembly via its interaction with TBP.