sentences:  This pausing is especially pronounced at nucleosomes, and arises in part through the polymerase entering a transcriptionally incompetent backtracked state.The duration of these pauses ranges from seconds to minutes or longer, and exit from long-lived pauses can be promoted by elongation factors such as TFIIS.This pausing is also sometimes used for proofreading; here the polymerase backs up, erases some of the RNA it has already made and has another go at transcription.