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J. Bacteriol., Apr 1995, 1655-1661, Vol 177, No. 7
RR Ariza, Z Li, N Ringstad and B Demple
Multiple antibiotic resistance in Escherichia coli can be mediated by
induction of the SoxS or MarA protein, triggered by oxygen radicals (in the
soxRS regulon) or certain antibiotics (in the marRAB regulon),
respectively. These small proteins (SoxS, 107 residues; MarA, 127 residues)
are homologous to the C terminus of the XylS-AraC family of proteins and
are more closely related to a approximately 100-residue segment in the N
terminus of Rob protein, which binds the right arm of the replication
origin, oriC. We investigated whether the SoxS-MarA homology in Rob might
extend to the regulation of some of the same inducible genes.
Overexpression of Rob indeed conferred multiple antibiotic resistance
similar to that known for SoxS and MarA (against chloramphenicol,
tetracycline, nalidixic acid, and puromycin), as well as resistance to the
superoxide-generating compound phenazine methosulfate. The Rob-induced
antibiotic resistance depended only partially on the micF antisense RNA
that down-regulates the OmpF outer membrane porin to limit antibiotic
uptake. Similar antibiotic resistance was conferred by expression of a Rob
fragment containing only the N-terminal 123 residues that constitute the
SoxS-MarA homology. Both intact Rob and the N-terminal fragment activated
expression of stress genes (inaA, fumC, sodA) but with a pattern distinct
from that found for SoxS and MarA. Purified Rob protein bound a DNA
fragment containing the micF promoter (50% bound at approximately 10(-9) M
Rob) as strongly as it did oriC, and it bound more weakly to DNA containing
the sodA, nfo, or zwf promoter (50% bound at 10(-8) to 10(-7) M).(ABSTRACT
TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Activation of multiple antibiotic resistance and binding of stress- inducible promoters by Escherichia coli Rob protein
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, Massachusetts 02115.
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