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2016 ; 63
(6
): 939-50
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RNA Polymerase Pausing during Initial Transcription
#MMPMID27618490
Duchi D
; Bauer DL
; Fernandez L
; Evans G
; Robb N
; Hwang LC
; Gryte K
; Tomescu A
; Zawadzki P
; Morichaud Z
; Brodolin K
; Kapanidis AN
Mol Cell
2016[Sep]; 63
(6
): 939-50
PMID27618490
show ga
In bacteria, RNA polymerase (RNAP) initiates transcription by synthesizing short
transcripts that are either released or extended to allow RNAP to escape from the
promoter. The mechanism of initial transcription is unclear due to the presence
of transient intermediates and molecular heterogeneity. Here, we studied initial
transcription on a lac promoter using single-molecule fluorescence observations
of DNA scrunching on immobilized transcription complexes. Our work revealed a
long pause ("initiation pause," ?20 s) after synthesis of a 6-mer RNA; such
pauses can serve as regulatory checkpoints. Region sigma 3.2, which contains a
loop blocking the RNA exit channel, was a major pausing determinant. We also
obtained evidence for RNA backtracking during abortive initial transcription and
for additional pausing prior to escape. We summarized our work in a model for
initial transcription, in which pausing is controlled by a complex set of
determinants that modulate the transition from a 6- to a 7-nt RNA.
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