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J. Bacteriol., 01 1995, 103-113, Vol 177, No. 1
M Ferrario, BR Ernsting, DW Borst, DE Wiese 2nd, RM Blumenthal and RG Matthews
The two major porins of Escherichia coli K-12 strains, OmpC and OmpF, are
inversely regulated with respect to one another. The expression of OmpC and
OmpF has been shown to be influenced by the leucine-responsive regulatory
protein (Lrp): two-dimensional gel electrophoresis of proteins from strains
with and strains without a functional Lrp protein revealed that OmpC
expression is increased in an lrp strain, while OmpF expression is
decreased. In agreement with these findings, we now present evidence that
transcriptional (operon) fusions of lacZ+ to ompC and micF are negatively
regulated by Lrp. Lrp binds specifically to the intergenic region between
micF and ompC, as indicated by mobility shift assays and by DNase I
footprinting. The expression of an ompF'-lacZ+ gene (translational) fusion
is increased 3.7-fold in an lrp+ background compared with an lrp
background, but expression of an ompF-lacZ+ operon fusion is not. Studies
of in vivo expression of the outer membrane porins during growth on glucose
minimal medium showed that the OmpF/OmpC ratio is higher in lrp+ strains
than it is in isogenic lrp strains. The effect of Lrp was not seen in a
strain containing a deletion of micF. Our studies suggest that the positive
effect of Lrp on OmpF expression stems from a negative effect of Lrp on the
expression of micF, an antisense RNA that inhibits ompF translation.
Copyright © 1995, American Society for Microbiology
The leucine-responsive regulatory protein of Escherichia coli negatively regulates transcription of ompC and micF and positively regulates translation of ompF
Department of Biological Chemistry, University of Michigan, Ann Arbor 48109-1055.
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