Analysis of TAF90 mutants displaying allele-specific and broad defects in transcription

Yeast TAF90p is a component of at least two transcription regulatory comple xes, the general transcription factor TFIID and the Spt-Ada-Gcn5 histone ac etyltransferase complex (SAGA). Broad transcription defects have been obser ved in mutants of other TAF(II)s shared by TFIID and SAGA but not in the on ly two TAF90 mutants isolated to date. Given that the numbers of mutants an alyzed thus far are small, we isolated and characterized 11 temperature-sen sitive mutants of TAF90 and analyzed their effects on transcription and int egrity of the TFIID and SAGA complexes. We found that the mutants displayed a variety of allele-specific defects in their ability to support transcrip tion and maintain the structure of the TFIID and SAGA complexes. Sequencing of the alleles revealed that all have mutations corresponding to the C ter minus of the protein, with most clustering within the conserved WD40 repeat s; thus, the C terminus of TAF90p is required for its incorporation into TF IID and function in SAGA. Significantly, inactivation of one allele, taf90- 20, caused the dramatic reduction in the levels of total mRNA and most spec ific transcripts analyzed. Analysis of the structure and/or activity of bot h TAF90p-containing complexes revealed that this allele is the most disrupt ive of all. Our analysis defines the requirement for the WD40 repeats in pr eserving TFIID and SAGA function, demonstrates that the defects associated with distinct mutations in TAF90 vary considerably, and indicates that TAF9 0 can be classified as a gene required for the transcription of a large num ber of genes.