TAFs revisited: more data reveal new twists and confirm old ideas

Synthesis of messenger RNA by RNA polymerase II requires the combined activ ities of more than 70 polypeptides. Coordinating the interaction of these p roteins is the basal transcription factor TFIID, which recognizes the core promoter and supplies a scaffolding upon which the rest of the transcriptio nal machinery can assemble. A multisubunit complex, TFIID consists of the T ATA-binding protein (TBP) and several TBP-associated factors (TAFs), whose primary sequences are well-conserved from yeast to humans. Data from recons tituted cell-free transcription systems and binary interaction assays sugge st that the TAF subunits can function as promoter-recognition factors, as c oactivators capable of transducing signals from enhancer-bound activators t o the basal machinery, and even as enzymatic modifiers of other proteins. W hether TAFs function similarly in vivo, however, has been an open question. Initial characterization of yeast bearing mutations in particular TAFs see mingly indicated that, unlike the situation in vitro, TAFs played only a mi nor role in transcriptional regulation in vivo. However, reconsideration of this data in light of more recent results from yeast and other organisms r eveals considerable convergence between the models derived from in vitro ex periments and those derived from in vivo studies. In particular, there is a n emerging consensus that TAFs represent one of several classes of coactiva tors that participate in transcriptional activation in vivo. (C) 2000 Publi shed by Elsevier Science B.V. All rights reserved.