Journal of Bacteriology, June 2000, p. 3055-3062, Vol. 182, No. 11
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
D-Dependent Gene Expression

Department of Biology, San Francisco State University, San Francisco, California 94132
Received 4 October 1999/Accepted 17 March 2000
The
D regulon of Bacillus subtilis is
composed of genes encoding proteins for flagellar synthesis, motility,
and chemotaxis. Concurrent analyses of
D protein levels
and flagellin mRNA demonstrate that sigD expression and
D activity are tightly coupled during growth in both
complex and minimal media, although they exhibit different patterns of
expression. We therefore used the
D-dependent flagellin
gene (hag) as a model gene to study the effects of
different nutritional environments on
D-dependent gene
expression. In complex medium, the level of expression of a
hag-lacZ fusion increased exponentially during the
exponential growth phase and peaked early in the transition state. In
contrast, the level of expression of this reporter remained constant
and high throughout growth in minimal medium. These results suggest the
existence of a nutritional signal(s) that affects sigD
expression and/or
D activity. This signal(s) allows for
nutritional repression early in growth and, based on reconstitution
studies, resides in the complex components of sporulation medium, as
well as in a mixture of mono-amino acids. However, the addition of
Casamino Acids to minimal medium results in a dose-dependent decrease
in hag-lacZ expression throughout growth and the
postexponential growth phase. In work by others, CodY has been
implicated in the nutritional repression of several genes. Analysis of
a codY mutant bearing a hag-lacZ reporter
revealed that flagellin expression is released from nutritional
repression in this strain, whereas mutations in the transition state
preventor genes abrB, hpr, and sinR
failed to elicit a similar effect during growth in complex medium.
Therefore, the CodY protein appears to be the physiologically relevant
regulator of hag nutritional repression in B. subtilis.
Present address: Department of Human Genetics, Roche Molecular
Systems, Alameda, Calif.
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