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Infect. Immun., 08 1997, 3091-3099, Vol 65, No. 8
AR Hoffmaster and TM Koehler
The Bacillus anthracis toxin genes, cya, lef, and pag, can be viewed as a
regulon, in which transcription of all three genes is activated in trans by
the same regulatory gene, atxA, in response to the same signal, CO2. In
atxA+ strains, toxin gene expression is increased 5- to 20-fold in cells
grown in 5% CO2 relative to cells grown in air. CO2- enhanced toxin gene
transcription is not observed in atx4-null mutants. Here, we used two
independent techniques to obtain evidence for additional CO2-induced
atxA-regulated genes. First, total protein preparations from atxA4+ and
atxA isolates grown in 5% CO2 and in air were examined by two-dimensional
electrophoresis. Comparison of the resulting protein patterns indicated
that synthesis of non-toxin proteins is influenced by growth in elevated
CO2 and the toxin gene regulator, atxA. Second, we generated random
transcriptional lacZ fusions in B. anthracis with transposon Tn917-LTV3.
Transposon- insertion libraries were screened for mutants expressing
CO2-enhanced atxA-dependent beta-galactosidase activity. DNA sequence
analysis of transposon insertion sites in 17 mutants carrying CO2- and
atxA- regulated fusions revealed 10 mutants carrying independent insertions
on the 185-kb toxin plasmid pXO1 which did not map to the toxin genes. The
tcr-lacZ fusion mutants (tcr for toxin coregulated) were Tox+, indicating
that these genes may not be involved in anthrax toxin gene activation. Our
data indicate a clear association of atxA with CO2- enhanced gene
expression in B. anthracis and provide evidence that atxA regulates genes
other than the structural genes for the anthrax toxin proteins.
Copyright © 1997, American Society for Microbiology
The anthrax toxin activator gene atxA is associated with CO2-enhanced non-toxin gene expression in Bacillus anthracis
Department of Microbiology and Molecular Genetics, Medical School, University of Texas-Houston, 77030, USA.
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