Distinct Mutations in Yeast TAFII25 Differentially Affect the Composition of TFIID and SAGA Complexes as Well as Global Gene Expression Patterns

Abstract

The RNA polymerase II transcription factor TFIID, composed of the TATA-binding protein (TBP) and TBP-associated factors (TAF_IIs), nucleates preinitiation complex formation at protein-coding gene promoters. SAGA, a second TAF_II-containing multiprotein complex, is involved in transcription regulation in Saccharomyces cerevisiae. One of the essential protein components common to SAGA and TFIID is yTAF_II25. We define a minimal evolutionarily conserved 91-amino-acid region of TAF_II25 containing a histone fold domain that is necessary and sufficient for growth in vivo. Different temperature-sensitive mutations of yTAF_II25 or chimeras with the human homologue TAF_II30 arrested cell growth at either the G₁ or G₂/M cell cycle phase and displayed distinct phenotypic changes and gene expression patterns. Immunoprecipitation studies revealed that TAF_II25 mutation-dependent gene expression and phenotypic changes correlated at least partially with the integrity of SAGA and TFIID. Genome-wide expression analysis revealed that the five TAF_II25 temperature-sensitive mutant alleles individually affect the expression of between 18 and 33% of genes, whereas taken together they affect 64% of all class II genes. Thus, different yTAF_II25 mutations induce distinct phenotypes and affect the regulation of different subsets of genes, demonstrating that no individual TAF_II mutant allele reflects the full range of its normal functions.