An RNA polymerase II holoenzyme that contains, in addition to RNA polymerase, a subset of the general transcription factors together with nine SRB proteins is described. This holoenzyme will selectively initiate transcription in vitro when supplemented with TATA-binding protein (TBP) and factor a (TFIIE). The SRB proteins act positively and negatively to regulate transcription initiation, at least in part, via functional interactions with RNA polymerase II.