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Journal of Bacteriology, August 2000, p. 4295-4303, Vol. 182, No. 15
Department of Microbiology, Dartmouth Medical
School, Hanover, New Hampshire 03755
Received 12 January 2000/Accepted 15 May 2000
H-NS is an abundant nucleoid-associated protein involved in the
maintenance of chromosomal architecture in bacteria. H-NS also has a
role in silencing the expression of a variety of environmentally regulated genes during growth under nonpermissive conditions. In this
study we demonstrate a role for H-NS in the negative modulation of
expression of several genes within the ToxR virulence regulon of
Vibrio cholerae. Deletion of hns resulted in
high, nearly constitutive levels of expression of the genes encoding
cholera toxin, toxin-coregulated pilus, and the ToxT virulence gene
regulatory protein. For the cholera toxin- and ToxT-encoding genes,
elevated expression in an hns mutant was found to occur in
the absence of the cognate activator proteins, suggesting that H-NS
functions directly at these promoters to decrease gene expression.
Deletion analysis of the region upstream of toxT suggests
that an extensive region located far upstream of the transcriptional
start site is required for complete H-NS-mediated repression of gene
expression. These data indicate that H-NS negatively influences
multiple levels of gene expression within the V. cholerae
virulence cascade and raise the possibility that the transcriptional
activator proteins in the ToxR regulon function to counteract the
repressive effects of H-NS at the various promoters as well as to
recruit RNA polymerase.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Vibrio cholerae H-NS Silences Virulence
Gene Expression at Multiple Steps in the ToxR Regulatory
Cascade
*
Corresponding author. Mailing address: Department of
Microbiology, HB7550, Dartmouth Medical School, Hanover, NH 03755. Phone: (603) 650-1632. Fax: (603) 650-1318. E-mail:
ronald.k.taylor{at}dartmouth.edu.
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