Dynamic turnover of paused Pol II complexes at human promoters.
Paused RNA polymerase II (Pol II) that piles up near most human promoters is the target of mechanisms that control entry into productive elongation. Whether paused Pol II is a stable or dynamic target remains unresolved. We report that most 5' paused Pol II throughout the genome is turned over within 2 min. This process is revealed under hypertonic conditions that prevent Pol II recruitment to promoters. This turnover requires cell viability but is not prevented by inhibiting transcription elongation, suggesting that it is mediated at the level of termination. When initiation was prevented by triptolide during recovery from high salt, a novel preinitiated state of Pol II lacking the pausing factor Spt5 accumulated at transcription start sites. We propose that Pol II occupancy near 5' ends is governed by a cycle of ongoing assembly of preinitiated complexes that transition to pause sites followed by eviction from the DNA template. This model suggests that mechanisms regulating the transition to productive elongation at pause sites operate on a dynamic population of Pol II that is turning over at rates far higher than previously suspected. We suggest that a plausible alternative to elongation control via escape from a stable pause is by escape from premature termination.
['Erickson|Benjamin|B|', 'Sheridan|Ryan M|RM|', 'Cortazar|Michael|M|', 'Bentley|David L|DL|']
D004224:Diterpenes D004852:Epoxy Compounds D045325:HCT116 Cells D006801:Humans D007552:Isotonic Solutions D010616:Phenanthrenes D011401:Promoter Regions, Genetic D012319:RNA Polymerase II D012462:Saline Solution, Hypertonic D061805:Transcription Elongation, Genetic D061785:Transcription Initiation, Genetic
transcription elongation Spt5 Pol II pausing transcription initiation transcriptional regulation