Affiliation:
1. Department of Microbiology and Molecular Genetics, the University of Texas—Houston Health Science Center Medical School, Houston, Texas 77030
Abstract
ABSTRACT
Expression of the structural genes for the anthrax toxin proteins is coordinately controlled by host-related signals, such as elevated CO
2
, and the
trans
-acting positive regulator AtxA. In addition to these requirements, toxin gene expression is under growth phase regulation. The transition state regulator AbrB represses
atxA
expression to influence toxin synthesis. During the late exponential phase of growth, when AbrB levels begin to decrease, toxin synthesis increases. Here we report that toxin gene expression also requires the presence of
sigH
, a gene encoding the RNA polymerase sigma factor associated with development in
Bacillus subtilis
. In the well-studied
B. subtilis
system, σ
H
is required for sporulation and other post-exponential-phase processes and is part of a feedback control pathway for
abrB
expression. Our data indicate that a
Bacillus anthracis sigH
-null mutant is asporogenous and toxin deficient. Yet the sigma factor is required for toxin gene expression in a manner that is independent of the pathway leading to post-exponential-phase gene expression. σ
H
positively controls
atxA
in an AbrB-independent manner. These findings, combined with previous observations, suggest that the steady-state level of
atxA
expression is critical for optimal toxin gene transcription. We propose a model whereby, under toxin-inducing growth conditions, control of toxin gene expression is fine-tuned by the independent effects of σ
H
and AbrB on the expression of
atxA
.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
39 articles.
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