IDENTIFICATION AND CHARACTERIZATION OF A TFIID-LIKE MULTIPROTEIN COMPLEX FROM SACCHAROMYCES-CEREVISIAE

Although the mechanisms of transcriptional regulation by RNA polymeras e II are apparently highly conserved from yeast to man, the identifica tion of a yeast TATA-binding protein (TBP)-TBP-associated factor (TAF( II)) complex comparable to the metazoan TFIID component of the basal t ranscriptional machinery has remained elusive. Here, we report the iso lation of a yeast TBP-TAF(II) complex which can mediate transcriptiona l activation by GAL4-VP16 in a highly purified yeast in vitro transcri ption system, We have cloned and sequenced the genes encoding four of the multiple yeast TAF(II) proteins comprising the TBP-TAF(II) multisu bunit complex and find that they are similar at the amino acid level t o both human and Drosophila TFIID subunits. Using epitope-tagging and immunoprecipitation experiments, we demonstrate that these genes encod e bona fide TAF proteins and show that the yeast TBP-TAF(II) complex i s minimally composed of TBP and seven distinct yTAF(II) proteins rangi ng in size from M(r) = 150,000 to M(r) = 25,000. In addition, by const ructing null alleles of the cloned TAF-encoding genes, we show that no rmal function of the TAF-encoding genes is essential for yeast cell vi ability.