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Journal of Bacteriology, October 2001, p. 5675-5683, Vol. 183, No. 19
Unité de Microbiologie et
Génétique, UMR CNRS 5122, Université Lyon 1, F-69622 Villeurbanne Cedex, France
Received 26 March 2001/Accepted 11 July 2001
The expression of the maltose system in Escherichia
coli is regulated at both transcriptional and
translational levels by the pH of the growth medium (pHo). With
glycerol as the carbon source, transcription of
malT, encoding the transcriptional activator of the
maltose regulon, is weaker in acidic medium than in alkaline medium. malT transcription became high, regardless of
the pHo, when glycerol-3-phosphate or succinate was used as the carbon source. Conversely, malT expression was low, regardless
of the pHo, when maltose was used as the carbon source. The
increase in malT transcription, associated with the pHo,
requires the presence of glycerol in the
growth medium and the expression of the glycerol kinase (GlpK). Changes
in the level of glpK transcription had a great
effect on malT transcription. Indeed, a
glpFKX promoter-down mutation has been isolated,
and in the presence of this mutation, malT
expression was increased. When glpK was expressed from a high-copy-number plasmid, the
glpK-dependent reduced expression of the maltose system
became effective regardless of the pHo. Analysis of this
repression showed that a malTp1 malTp10 promoter, which
is independent of the cyclic AMP (cAMP)-cAMP receptor protein (CRP) complex, was no longer repressed by glpFKX
amplification. Thus, GlpK-dependent repression of the maltose
system requires the cAMP-CRP complex. We propose that the pHo may
affect a complex interplay between GlpK, the
phosphotransferase-mediated uptake of glucose, and the adenylate cyclase.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.19.5675-5683.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
External-pH-Dependent Expression of the Maltose Regulon
and ompF Gene in Escherichia coli Is
Affected by the Level of Glycerol Kinase, Encoded by
glpK

*
Corresponding author. Mailing address: Unité de
Microbiologie et Génétique, UMR CNRS 5122, Bât
A. Lwoff, Université Lyon 1, F-69622 Villeurbanne Cedex, France.
Phone: (33) 472 431 621. Fax: (33) 472 432 686. E-mail:
plaloi{at}biomserv.univ-lyon1.fr.
Present address: INSERM U447, Institut de Biologie de Lille,
Institut Pasteur de Lille, F-59019 Lille Cedex, France.
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