An RNA polymerase II holoenzyme responsive to activators

Abstract

RNA POLYMERASE II requires multiple general transcription factors to initiate site-specific transcription^1–3. These proteins can assemble in an ordered fashion onto promoter DNA in vitro^2–8, and such ordered assembly may occur in vivo (Fig. la). Some general transcription factors can interact with RNA polymerase II in the absence of DNA^3,9–15, however, suggesting that RNA polymerase II may also assemble into a multi-component complex containing a subset of initiation factors before binding to promoter DNA (Fig. Ib). Here we present evidence from the yeast Saccharo-myces cerevisiae for such an RNA polymerase II holoenzyme, a multi-subunit complex containing roughly equimolar amounts of RNA polymerase II, a subset of general transcription factors, and SRB regulatory proteins. Transcription by this holoenzyme is stimulated by the activator protein GAL4-VP16, a feature not observed with purified RNA polymerase II and general transcription factors alone. We propose that the holoenzyme is a form of RNA polymerase II readily recruited to promoters in vivo.