Transcription at Pol II promoters. (a) The phases of transcription by Pol II—assembly, initiation, elongation, and termination—are associated with characteristic proteins, as described in the text. The ordered assembly and dissociation of these factors drives the process forward. (b) After association of transcription factors with Pol II on DNA to form an open initiation complex, some factors dissociate to enable transcription elongation, termination, and recycling.