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J. Bacteriol., May 1995, 2328-2334, Vol 177, No. 9
O Lomovskaya, K Lewis and A Matin
The emrAB locus of Escherichia coli encodes a multidrug resistance pump
that protects the cell from several chemically unrelated antimicrobial
agents, e.g., the protonophores carbonyl cyanide m- chlorophenylhydrazone
(CCCP) and tetrachlorosalicyl anilide and the antibiotics nalidixic acid
and thiolactomycin. The mprA gene is located immediately upstream of this
locus and was shown to be a repressor of microcin biosynthesis (I. del
Castillo, J. M. Gomez, and F. Moreno, J. Bacteriol. 173:3924-3929, 1991).
There is a putative transcriptional terminator sequence between the mprA
and emrA genes. To locate the emr promoter, single-copy lacZ operon fusions
containing different regions of the emr locus were made. Only fusions
containing the mprA promoter region were expressed. mprA is thus the first
gene of the operon, and we propose that it be renamed emrR. Overproduction
of the EmrR protein (with a multicopy vector containing the cloned emrR
gene) suppressed transcription of the emr locus. A mutation in the emrR
gene led to overexpression of the EmrAB pump and increased resistance to
antimicrobial agents. CCCP, nalidixic acid, and a number of other
structurally unrelated chemicals induced expression of the emr genes, and
the induction required EmrR. We conclude that emrRAB genes constitute an
operon and that EmrR serves as a negative regulator of this operon. Some of
the chemicals that induce the pump serve as its substrates, suggesting that
their extrusion is the natural function of the pump.
Copyright © 1995, American Society for Microbiology
EmrR is a negative regulator of the Escherichia coli multidrug resistance pump EmrAB
Department of Microbiology and Immunology, Stanford University School of Medicine, California 94305-5402, USA.
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