The TBP associated factor "yTaf II 19p" functionally interacts with components of the global transcriptional regulator "the Ccr4-Not complex" and physically interacts with the Not5 subunit
Résumé
The Saccharomyces cerevisiae HIS3 gene is a model system to characterize transcription initiation from different types of core promoters. The NOT genes were identified by mutations that preferentially increased transcription of the HIS3 promoter lacking a canonical TATA sequence. They encode proteins associated in a complex that also contains the Caf1 and Ccr4 proteins. It has been suggested that the Ccr4-Not complex represses transcription by inhibiting factors more specifically required for promoters lacking a TATA sequence. A potential target is the yTaf II 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 phenotypes when combined with not4 or specific not5 alleles. Inactivation of yTaf II 19p by shifting these mutants to the restrictive temperature led to a more 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 II 19p and Not5p could interact. Finally, we found by the two-hybrid assay that yTaf II 19p also interacted with many components of the Ccr4-Not complex. Taken together, our results provide evidence that interactions between Not5p and yTaf II 19p may be involved in transcriptional regulation by the Ccr4-Not complex.
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