The TATA-binding protein-associated factor yTaf(II)19p functionally interacts with components of the global transcriptional regulator Ccr4-not complex and physically interacts with the NOT5 subunit

The Saccharomyces cerevisiae HIS3 gene is a model system to characterize tr anscription initiation from different types of core promoters. The NOT gene s were identified by mutations that preferentially increased transcription of the HIS3 promoter lacking a canonical TATA sequence. They encode protein s associated in a complex that also contains the Caf1 and Ccr4 proteins. It has been suggested that the Ccr4-Not complex represses transcription by in hibiting factors more specifically required for promoters lacking a TATA se quence. A potential target is the yTaf(11)19 subunit of TFIID, which, when depleted, leads to a preferential decrease of HIS3 TATA-less transcription. We isolated conditional taf19 alleles that display synthetic growth phenot ypes when combined with not4 or specific not5 alleles. Inactivation of yTaf (11)19p by shifting these mutants to the restrictive temperature led to a m ore rapid and striking decrease in transcription from promoters that do not contain a canonical TATA sequence. We demonstrated by the two-hybrid assay and directly in vitro that yTaf(11)19p and Not5p could interact. Finally, we found by the two-hybrid assay that yTaf(11)19p also interacted with many components of the Ccr4 Not complex, Taken together, our results provide ev idence that interactions between Not5p and yTaf(11)19p may be involved in t ranscriptional regulation by the Ccr4-Not complex.