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Hoffmaster, AR and Koehler, TM (1997) The anthrax toxin activator gene atxA is associated with CO2-enhanced non-toxin gene expression in Bacillus anthracis. Infect. Immun. 65:3091-9


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.


PubMed PMC175436


Antigens, Bacterial; Bacillus anthracis/genetics; Bacillus anthracis/growth & development; Bacillus anthracis/pathogenicity; Bacterial Proteins/biosynthesis; Bacterial Toxins/genetics; Base Sequence; Carbon Dioxide; Cloning, Molecular; Gene Expression Regulation, Bacterial; Genes, Bacterial; Lac Operon; Molecular Sequence Data; Mutation; Transcription, Genetic; Transcriptional Activation; Virulence



Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status


GO:0010628: positive regulation of gene expression



Table 2. Screen for Tn917-LTV3 insertion mutants harboring CO2-enhanced atxA-dependent transcriptional lacZ fusions TABLE 3. Complementation of the atxA tcr-lacZ isolatesa



GO:0010037: response to carbon dioxide



Fig. 1b box A. Antibody to EF was not available. Boxes B, C, and D contain spots representing proteins which were CO2 and/or atxA dependent yet did not react with anti-toxin antisera. Boxes B and C show four spots which appear to be weakly atxA and CO2 dependent. Box D shows two spots which are atxA dependent but not CO2 dependent. These data indicate that synthesis of nontoxin proteins is influenced by growth in elevated CO2 and by the toxin gene regulator, AtxA.


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