Identification of a yeast transcription factor IID subunit, TSG2/TAF48

The RNA polymerase II general transcription factor TFIID is a complex conta ining the TATA-binding protein (TBP) and associated factors (TAFs). We have used a mutant allele of the gene encoding yeast TAF(II)68/61p to analyze i ts function in vivo. We provide biochemical and genetic evidence that the C -terminal cw-helix of TAF(II)68/61p is required for its direct interaction with TBP, the stable incorporation of TBP into the TFIID complex, the integ rity of the TFIID complex, and the transcription of most genes in vivo. Thi s is the first evidence that a yeast TAF(II) other than TAF(II)145/130 inte racts with TBP, and the implications of this on the interpretation of data obtained studying TAF(II) mutants in vivo are discussed. We have identified a high copy suppressor of the TAF68/61 mutation, TSG2, that has sequence s imilarity to a region of the SAGA subunit Ada1. We demonstrate that it dire ctly interacts with TAF(II)68/61p in vitro, is a component of TFIID, is req uired for the stability of the complex in vivo, and is necessary for the tr anscription of many yeast genes. On the basis of these functions, we propos e that Tsg(2)/TAF(II)48p is the histone 2A-like dimerization partner for th e histone 2B-like TAF(II)68/61p in the yeast TFIID complex.