Mechanisms of transcription complex assembly.

Gene-specific activators control the access of RNA polymerase II (pol II) to promoters in several ways: by chromatin rearrangement involving an ATP-dependent SWI-SNF complex; by the synergistic recruitment of transcription factor IID (TFIID); and by either the sequential recruitment of basal transcription factors and pol II or the recruitment of a preformed pol II holoenzyme which includes most of the basal factors. One of the most significant recent developments has been the demonstration that distinct subunits of TFIID (namely subunits of the TATA-binding protein associated factor) target different activators, basal factors, and core promoter elements.