THE YEAST TATA-BINDING PROTEIN (TBP) CORE DOMAIN ASSEMBLES WITH HUMANTBP-ASSOCIATED FACTORS INTO A FUNCTIONAL TFIID COMPLEX

In mammalian and Drosophila cells, the central RNA polymerase II gener al transcription factor TFIID is a multisubunit complex containing the TATA-binding protein (TBP) and TBP-associated factors (TAFs) bound to the conserved TBP carboxy-terminal core domain. TBP also associates w ith alternative TAFs in these cells to form general transcription fact ors required for initiation by RNA polymerases I and III. Although ext racts of human HeLa cells contain little TBP that is not associated wi th TAFs, free TBP is readily isolated from yeast cell extracts. Howeve r, recent studies indicate that yeast TBP can also interact with other yeast polypeptides to form multiprotein complexes. We established sta ble human HeLa cell lines expressing yeast TBP and several yeast-human TBP hybrids to study TBP-TAF interactions. We found that the yeast TB P core domain assembles with a complete set of human TAFs into a stabl e TFIID complex that can support activated transcription in vitro. The fact that the yeast TBP core, which differs from human TBP core in si milar to 20% of its amino acid residues, has the structural features r equired to form a stable complex with human TAFs implies that Saccharo myces cerevisiae probably contains TAFs that are structurally and func tionally analogous to human TAFs. Surprisingly, the nonconserved amino terminus of yeast TBP inhibited association between the yeast core do main and human TAFs.