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Journal of Bacteriology, November 1998, p. 5875-5884, Vol. 180, No. 22
Department of Molecular Biology, Princeton
University, Princeton, New Jersey 08544,1
and
Department of Microbiology and Immunology, Uniformed
Services University of the Health Sciences, Bethesda, Maryland
20814-47992
Received 7 July 1998/Accepted 18 September 1998
In Escherichia coli, transcription of the
degP locus, which encodes a heat-shock-inducible
periplasmic protease, is controlled by two parallel signal transduction
systems that each monitor extracytoplasmic protein physiology. For
example, the heat-shock-inducible sigma factor,
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Accumulation of the Enterobacterial Common
Antigen Lipid II Biosynthetic Intermediate Stimulates
degP Transcription in Escherichia
coli


E,
controls degP transcription in response to the
overproduction and folded state of various extracytoplasmic proteins.
Similarly, the CpxA/R two-component signal transduction system
increases degP transcription in response to the
overproduction of a variety of extracytoplasmic proteins. Since
degP transcription is attuned to the physiology of
extracytoplasmic proteins, we were interested in identifying negative
transcriptional regulators of degP. To this end, we
screened for null mutations that increased transcription from a strain
containing a degP-lacZ reporter fusion. Through this
approach, we identified null mutations in the wecE,
rmlAECA, and wecF loci that
increase degP transcription. Interestingly, each of these
loci is responsible for synthesis of the enterobacterial common antigen
(ECA), a glycolipid situated on the outer leaflet of the outer membrane
of members of the family Enterobacteriaceae. However, these
null mutations do not stimulate degP transcription by
eliminating ECA biosynthesis. Rather, the wecE,
rmlAECA, and wecF null mutations
each impede the same step in ECA biosynthesis, and it is the
accumulation of the ECA biosynthetic intermediate, lipid II, that
causes the observed perturbations. For example, the lipid
II-accumulating mutant strains each (i) confer upon E. coli
a sensitivity to bile salts, (ii) confer a sensitivity to the synthesis
of the outer membrane protein LamB, and (iii) stimulate both the Cpx
pathway and
E activity. These phenotypes suggest that
the accumulation of lipid II perturbs the structure of the bacterial
outer membrane. Furthermore, these results underscore the notion that
although the Cpx and
E systems function in parallel to
regulate degP transcription, they can be simultaneously
activated by the same perturbation.
*
Corresponding author. Mailing address: Department of
Molecular Biology, Princeton University, Princeton, NJ 08544. Phone: (609) 258-5899. Fax: (609) 258-2957. E-mail:
tsilhavy{at}molbio.princeton.edu.
Present address: Department of Molecular and Cellular Biology,
Harvard University, Cambridge, MA 02138.
Present address: University of Texas Southwestern Medical School,
Dallas, TX 75235.
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