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J. Bacteriol., Aug 1995, 4216-4223, Vol 177, No. 15
WB Snyder, LJ Davis, PN Danese, CL Cosma and TJ Silhavy
The LamB-LacZ-PhoA tripartite fusion protein is secreted to the periplasm,
where it exerts a toxicity of unknown origin during high- level synthesis
in the presence of the inducer maltose, a phenotype referred to as maltose
sensitivity. We selected multicopy suppressors of this toxicity that allow
growth of the tripartite fusion strains in the presence of maltose. Mapping
and subclone analysis of the suppressor locus identified a previously
uncharacterized chromosomal region at 4.7 min that is responsible for
suppression. DNA sequence analysis revealed a new gene with the potential
to code for a protein of 236 amino acids with a predicted molecular mass of
25,829 Da. The gene product contains an amino-terminal signal sequence to
direct the protein for secretion and a consensus lipoprotein modification
sequence. As predicted from the sequence, the suppressor protein is labeled
with [3H]palmitate and is localized to the outer membrane. Accordingly, the
gene has been named nlpE (for new lipoprotein E). Increased expression of
NlpE suppresses the maltose sensitivity of tripartite fusion strains and
also the extracytoplasmic toxicities conferred by a mutant outer membrane
protein, LamBA23D. Suppression occurs by activation of the Cpx
two-component signal transduction pathway. This pathway controls the
expression of the periplasmic protease DegP and other factors that can
combat certain types of extracytoplasmic stress.
Copyright © 1995, American Society for Microbiology
Overproduction of NlpE, a new outer membrane lipoprotein, suppresses the toxicity of periplasmic LacZ by activation of the Cpx signal transduction pathway
Department of Molecular Biology, Princeton University, New Jersey 08544, USA.
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