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 or Y69A/W76A mutant was lethal in Saccharomyces cerevisiae, while the Y69F/W76F mutant exhibited extremely slow growth at 30°C. Both the Y69A and W76A mutants were conditionally lethal at higher temperatures. Light microscopy indicated that viable toa2 mutant strains accumulate as equal-size dumbbells and multibudded clumps. Transcription of the cell cycle-regulatory genes CLB1, CLB2, CLN1, and CTS1 was significantly reduced in the toa2 mutant strains, while the noncycling genes PMA1 and ENO2 were only modestly affected, suggesting that these toa2 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 of CUP1, PHO5, TRP3, and GAL1 gene activation, but the constitutive expression of DED1 was significantly reduced. Activator-induced start site expression for HIS3, GAL80, URA1, and URA3 promoters was defective in toa2 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 toa2 mutants 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 in S. cerevisiae.The RNA polymerase II general transcription factors are an evolutionarily conserved set of proteins required for the regulation and recognition of specific promoter start sites (reviewed in references 56 and 60). In higher eukaryotes, the general transcription factor IID (TFIID) binds to core promoter elements and can nucleate the assembly of an active preinitiation complex in vitro (reviewed in reference 10). TFIID consists of the TATA binding protein (TBP) and TBPassociated factors (TAF II s), which modify the promoter recognition and transcriptional activities of TBP (reviewed in reference 75). In addition to the TAF II s, multiple other factors can associate with TBP and regulate transcription initiation by modulating the binding of TBP to the core promoter (5,19,27,35,48,52). The general transcription factor IIA (TFIIA) is a positive modulator of TBP binding to TATA box elements and is essential for regulated transcription in vitro. However, the precise function and general requirement for a TFIIA-TBP association in vivo have not been completely ...

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