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 fao tors (TAF(II)s). One or more TAF(II)s are coactivators that are required for activated but not basal transcription(1-3). The eukaryotic transcription machinery is highly conserved and it is therefore puzzling that TAF(II)s have aot been identified in yeast. Here we use TBP as a protein-affinity ligand to isolate from yeast a multi-subunit 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 Saccharomyces cerevisiae.