IDENTIFICATION OF THE GENE (SSU71 TFG1) ENCODING THE LARGEST SUBUNIT OF TRANSCRIPTION FACTOR TFIIF AS A SUPPRESSOR OF A TFIIB MUTATION IN SACCHAROMYCES-CEREVISIAE/

Mutations in the Saccharomyces cerevisiae SSU71 gene were isolated as suppressors of a transcription factor TFIIB defect that confers both a cold-sensitive growth defect and a downstream shift in transcription start-site selection at the cyc1 locus. The ssu71-1 suppressor not onl y suppresses the conditional phenotype but also restores the normal pa ttern of transcription initiation at cyc1. In addition, the ssu71-1 su ppressor confers a heat-sensitive phenotype that is dependent upon the presence of the defective form of TFIIB. Molecular and genetic analys is of the cloned SSU71 gene demonstrated that SSU71 is a single-copy e ssential gene encoding a highly charged protein with a molecular mass of 82,194 daltons. Comparison of the deduced Ssu71 amino acid sequence with the protein data banks revealed significant similarity to RAP74, the larger subunit of the human general transcription factor TFIIF. M oreover, Ssu71 is identical to p105, a component of yeast TFIIF. Taken together, these data demonstrate a functional interaction between TFI IB and the large subunit of TFIIF and that this interaction can affect start-site selection in vivo.