ACTIVATION OF TRANSCRIPTION IN-VITRO BY RECRUITMENT OF THE YEAST RNA-POLYMERASE-II HOLOENZYME

It has been argued that many transcriptional activators work by ''recr uitment,'' that is, by helping the transcriptional machinery bind stab ly to DNA. We demonstrate here a realization of a strong prediction of this idea in an in vitro transcription reaction performed with purifi ed yeast RNA polymerase II holoenzyme and a classical transcriptional activator. We show that the level of transcription reached by the acti vator working on low concentrations of holoenzyme can also be reached in the absence of activator by raising the holoenzyme concentration, a nd that under that condition the activator has no further stimulatory effect. We also show, in agreement with another prediction of the recr uitment model, that in a reaction using a holoenzyme purified from cel ls bearing the ''P'' mutation, transcription is stimulated by a DNA-te thered peptide that binds the mutant holoenzyme component Gal11P but t hat lacks a classical activating region.