EFFECTS OF ACTIVATION-DEFECTIVE TBP MUTATIONS ON TRANSCRIPTION INITIATION IN YEAST

TRANSCRIPTION initiation by RNA polymerase II is effected by an ordere d series of general factor interactions with core promoter elements (l eading to basal activity) and further regulated by gene-specific facto rs acting from distal elements(1). Both the general factor TFIID (refs 2,3), including the constituent TBP (TATA-binding polypeptide)(4-7) a nd associated factors(8), and the interacting factor TFIIB (refs 9-11) have been implicated as targets for various activators. Towards an un derstanding of the basis for activator function, including the multipl icity of TBP interactions, we have now identified mutations in yeast T BP that selectively block activator (GAL4-VP16)-dependent but not basa l transcription. We further show an effect of GAL4-VP16 on TFIIB recru itment to early preinitiation complexes, and that recruitment is disru pted by TBP mutations that impair its interactions with VP16 (L114K), TFIIB (L189K) or an unidentified component (K211L). Thus, GAL4-VP16 fu nction seems to involve both direct interactions with TBP and a corres ponding induction (or stabilization) of an activation-specific TBP-TFI Ib-promoter complex.