Coordinated regulation of gene expression by E ... - Jacobs University

DISCUSSION
which both stabilizes the polymerase–promoter interaction and provides a nucleation
point for strand separation during promoter opening. At the tyrT promoter contacts in
the -10 region are facilitated by negative supercoiling [Pemberton et al., 2002] and
untwisting by FIS binding to the UAS [Muskhelishvili et al., 1997 and this work]. FIS
can also alleviate the inhibitory effect of ppGpp on transcription from the wild-type tyrT
promoter in vitro [Lazarus & Travers, 1993]. One, at least, of the mutations tested,
tyrTD, is insensitive to inhibition by ppGpp in vivo and in vitro [Lamond & Travers,
1985; Travers, 1980]. Taken as a whole these observations imply that for transcription
initiation at stable RNA promoters there is a mechanistic connection involving not only
high negative superhelicity and ppGpp levels, as previously suggested by Ohlsen &
Gralla [Ohlsen and Gralla, 1992] and by Figueroa-Bossi et al. [Figueroa-Bossi et al.,
1998] but also FIS. Together these parameters act to maintain tightly controlled levels
of transcription.
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