STIMULATION OF RNA-POLYMERASE-II TRANSCRIPTION INITIATION BY RECRUITMENT OF TBP IN-VIVO

EUKARYOTIC transcriptional activators may stimulate RNA polymerase II activity by promoting assembly of preinitiation complexes on promoters through their interactions with one or more components of the basal m achinery(1,2). On the basis of its central role in initiating transcri ption-complex formation upon binding to the TATA box, the general tran scription factor TFIID, which includes the TATA-binding protein (TBP) and several TBP-associated factors(3-5), has been implicated as a targ et for activators. Consistent with this idea, an increasing number of activators have been reported to bind directly to TBP6-9. To assess th e functional importance of these in vitro interactions for transcripti onal regulation in vivo, we made use of a novel strategy in yeast to s how that a physical interaction with TBP is sufficient for a sequence- specific DNA-binding protein to increase initiation of transcription b y RNA polymerase II. These results imply that binding of TFIID to prom oter elements is a limiting step in transcription complex assembly in vivo.