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Association of Transcription Factor IIA with TATA Binding Protein Is Required for Transcriptional Activation of a Subset of Promoters and Cell Cycle Progression inSaccharomyces cerevisiae

ABSTRACT The general transcription factor IIA (TFIIA) interacts with the TATA binding protein (TBP) and promoter DNA to mediate transcription activation in vitro. To determine if this interaction is generally required for activation of all class II genes in vivo, we have constructed substitution mutations in yeast TFIIA which compromise its ability to bind TBP. Substitution mutations in the small subunit of TFIIA (Toa2) at residue Y69 or W76 significantly impaired the ability of TFIIA to stimulate TBP-promoter binding in vitro. Gene replacement of wild-type TOA2 with a W76E orY69A/W76A mutant was lethal in Saccharomyces cerevisiae, while the Y69F/W76F mutant exhibited extremely slow growth at 30°C. Both the Y69A andW76A mutants were conditionally lethal at higher temperatures. Light microscopy indicated that viable toa2mutant strains accumulate as equal-size dumbbells and multibudded clumps. Transcription of the cell cycle-regulatory genesCLB1, CLB2, CLN1, andCTS1 was significantly reduced in the toa2mutant strains, while the noncycling genes PMA1 andENO2 were only modestly affected, suggesting that thesetoa2 mutant alleles disrupt cell cycle progression. The differential effect of these toa2 mutants on gene transcription was examined for a number of other genes.toa2 mutant strains supported high levels ofCUP1, PHO5, TRP3, andGAL1 gene activation, but the constitutive expression ofDED1 was significantly reduced. Activator-induced start site expression for HIS3, GAL80,URA1, and URA3 promoters was defective intoa2 mutant strains, suggesting that the TFIIA-TBP complex is important for promoters which require an activator-dependent start site selection from constitutive to regulated expression. We present evidence to indicate that transcription defects in toa2mutants can be both activator and promoter dependent. These results suggest that the association of TFIIA with TBP regulates activator-induced start site selection and cell cycle progression inS. cerevisiae.