Affiliation:
1. Department of Biology, San Francisco State University, San Francisco, California 94132
2. Department of Biology, University of Texas, El Paso, Texas 79968
Abstract
ABSTRACT
Expression of the σ
D
-dependent flagellin gene,
hag
, is repressed by the CodY protein in nutrient-rich environments. Analysis of a
codY
mutant bearing a
hag-lacZ
reporter suggests that the availability of amino acids in the environment is the specific signal that triggers this repression. Further,
hag-lacZ
expression appears to be sensitive to intracellular GTP levels, as demonstrated by increased expression upon addition of decoyinine. This result is consistent with the postulate that the availability of amino acids in the environment effects intracellular GTP levels through the stringent response. However, the levels of
hag-lacZ
measured upon the addition of subsets of amino acids suggest an additional mechanism(s). CodY is a DNA binding protein that could repress flagellin expression directly by binding to the
hag
promoter region, or indirectly by binding to the
fla/che
promoter region that governs expression of the σ
D
transcriptional activator required for
hag
gene expression. Using an electrophoretic mobility shift assay, we have demonstrated that purified CodY protein binds specifically to both the
hag
and
fla/che
promoter fragments. Additionally, CodY acts as a nutritional repressor of transcription from the
fla/che
promoter region that contains two functional promoters. CodY binds to both the σ
D
- and σ
A
-dependent promoters in this region, as demonstrated by DNase I footprint analyses. Footprint analyses of the
hag
gene demonstrated that CodY binds downstream of its σ
D
-dependent promoter. Taken together, these results identify new members of the CodY regulon that encode motility functions in
Bacillus subtilis
and are controlled by the σ
D
alternate sigma factor.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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