Promoter-proximal stalling results from the inability to recruit transcription factor IIH to the transcription complex and is a regulated event

Promoter-proximal stalling, a general phenomenon observed during the expression of many RNA polymerase II transcribed genes, is dependent on transcription factor IIH (TFIIH). Reactions lacking TFIIH initiated transcription, but the transcription complex encountered a block to elongation proximal to the promoter. The accumulation of promoter-proximal stalled complexes was reduced in the presence of TFIIH and efficient escape from this site also required an activator. Promoter-proximal stalled complexes could not be induced to resume elongation. Our results indicate that effective recruitment of TFIIH into transcription complexes is achieved during formation of the preinitiation complex at the promoter. The studies establish that promoter clearance is a regulated event that requires TFIIH.