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, τ60, present in affinity-purified TFIIIC. Hemagglutinin-tagged variants of τ60 were found to be part of TFIIIC-tDNA complexes and to reside at least in part in the downstream DNA-binding domain τB. Unexpectedly, the thermosensitive phenotype of N-terminally tagged τ60 was suppressed by overexpression of τ95, which belongs to the τA domain, and by two TFIIIB components, TATA-binding protein (TBP) and B"/TFIIIB90 (but not by TFIIIB70). Mutant TFIIIC was deficient in the activation of certain tRNA genes in vitro, and the transcription defect was selectively alleviated by increasing TBP concentration. Coimmunoprecipitation experiments support a direct interaction between TBP and τ60. It is suggested that τ60 links τA and τB domains and participates in TFIIIB assembly via its interaction with TBP.