Yeast TAF_IIs in a multisubunit complex required for activated transcription

IN higher eukaryotes the RNA polymerase II transcription factor TFIID is composed of a TATA-box-binding protein (TBP) and a set of tightly bound polypeptides, designated TBP-associated factors (TAF_II^S). One or more TAF_II^S are coactivators that are required for activated but not basal transcription^1-3. The eukary-otic transcription machinery is highly conserved and it is therefore puzzling that TAF_II^S have not been identified in yeast. Here we use TBP as a protein-affinity ligand to isolate from yeast a multisubunit complex that is required specifically for activated transcription by RNA polymerase II. Microsequence analysis and cloning of two subunits of this complex reveal that they are the homologues of known mammalian and Drosophila TAF_II ^S. The genes encoding these two yeast TAF_II^S are essential, suggesting that activated transcription is required for viability of Saccharo-myces cerevisiae.