Requirement for yeast TAF145 function in transcriptional activation of theRPS5 promoter that depends on both core promoter structure and upstream activating sequences

The general transcription factor TFIID has been shown to be involved in bot h core promoter recognition and the transcriptional activation of eukaryoti c genes. We recently isolated TAF145 (one of TFIID subunits) temperature-se nsitive mutants in yeast, in which transcription of the TUB2 gene is impair ed at restrictive temperatures due to a defect in core promoter recognition . Here, we show in these mutants that the transcription of the RPS5 gene is impaired, mostly due to a defect in transcriptional activation rather than to a defect in core promoter recognition, although the latter is slightly affected as well. Surprisingly, the RPS5 core promoter can be activated by various activation domains fused to a GAL4 DNA binding domain, but not by t he original upstream activating sequence (UAS) of the RPS5 gene. In additio n, a heterologous CYC1 core promoter can be activated by RPS5-UAS at normal levels even in these mutants. These observations indicate that a distinct combination of core promoters and activators may exploit alternative activa tion pathways that vary in their requirement for TAF145 function. In additi on, a particular function of TAF145 that is deleted in our mutants appears to be involved in both core promoter recognition and transcriptional activa tion.