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E. coli NusG inhibits backtracking and accelerates pause-free transcription by promoting forward translocation of RNA polymerase.

Abstract：

:NusG is an essential transcription factor in Escherichia coli that is capable of increasing the overall rate of transcription. Transcript elongation by RNA polymerase (RNAP) is frequently interrupted by pauses of varying durations, and NusG is known to decrease the occupancy of at least some paused states. However, it has not been established whether NusG enhances transcription chiefly by (1) increasing the rate of elongation between pauses, (2) reducing the lifetimes of pauses, or (3) reducing the rate of entry into paused states. Here, we studied transcription by single molecules of RNAP under various conditions of ribonucleoside triphosphate concentration, applied load, and temperature, using an optical trapping assay capable of distinguishing pauses as brief as 1 s. We found that NusG increases the rate of elongation, that is, the pause-free velocity along the template. Because pauses are off-pathway states that compete with elongation, we observed a concomitant decrease in the rate of entry into short-lifetime, paused states. The effects on short pauses and elongation were comparatively modest, however. More dramatic was the effect of NusG on suppressing entry into long-lifetime ("stabilized") pauses. Because a significant fraction of the time required for the transcription of a typical gene may be occupied by long pauses, NusG is capable of exerting a significant modulatory effect on the rates of RNA synthesis. The observed properties of NusG were consistent with a unified model where the function of this accessory factor is to promote transcriptionally downstream motion of the enzyme along the DNA template, which has the effect of forward-biasing RNAP from the pre-translocated state toward the post-translocated state.

journal_name

J Mol Biol

journal_title

Journal of molecular biology

authors

Herbert KM,Zhou J,Mooney RA,Porta AL,Landick R,Block SM

doi

10.1016/j.jmb.2010.03.051

subject

Has Abstract

pub_date

2010-05-28 00:00:00

pages

17-30

issue

eissn

0022-2836

issn

1089-8638

pii

S0022-2836(10)00326-8

journal_volume

399

pub_type

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E. coli NusG inhibits backtracking and accelerates pause-free transcription by promoting forward translocation of RNA polymerase.