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- Title
Cross-talk to the genes for Bacillus anthracis capsule synthesis by atxA, the gene encoding the frans-activator of anthrax toxin synthesis.
- Authors
Uchida, Ikuo; Makino, Sou-ichi; Sekizaki, Tsutomu; Terakado, Nobuyuki
- Abstract
The two major virulence factors of <em>Bacillus anthracis</em> are the tripartite toxin and the poLyglutamate capsule, which are encoded by genes on the large plasmids, pXO1 and pXO2, respectively. The genes <em>atxA</em>, located on pXO1, and <em>acpA</em>, located on pXO2, encode positive <em>trans</em>-acting proteins that are involved in bicarbonate-mediated regulation of toxin and capsule production, respectively. A derivative strain cured of pXO1 produced less capsular substance than the parent strain harbouring both pXO1 and pXO2, and electroporation of the strain cured of Pxo1 with a plasmid containing the cloned <em>atxA</em> gene resulted in an increased level of capsule production. An <em>acpA</em>-null mutant was complemented by not only <em>acpA</em> but also the <em>atxA</em> gene. The <em>cap</em> region, which is essential for encapsulation, contains three genes <em>capB</em>, <em>capC</em>, and <em>capA</em>, arranged in that order. The <em>atxA</em> gene stimulated capsule synthesis from the cloned <em>cap</em> region. Transcriptional analysis of <em>cap</em> by RNA slot-blot hybridization and primer-extension analysis revealed that <em>atxA</em> activated expression of <em>cap in trans</em> at the transcriptional level. These results indicate that cross-talk occurs, in which the pXO1-located gene, <em>atxA</em>, activates transcription of the <em>cap</em> region genes located on pXO2. We identified two major apparent transcriptional start sites, designated P1 and P2, located at positions 731 bp and 625 bp, respectively, upstream of the translation-initiation codon of <em>capB</em>. Transcription initiated from P1 and P2 was activated by both <em>atxA</em> and <em>acpA</em>, and activation appeared to be stimulated by bicarbonate. Deletion analysis of the upstream region of the <em>cap</em> promoter revealed that activation by both <em>atxA</em> and <em>acpA</em> required a DNA segment of 70 bp extending upstream of the P1 site. These results suggest that cross-talk by <em>atxA</em> to the genes encoding capsule synthesis is caused by the interaction of the <em>atxA</em> gene product with a regulatory sequence upstream of <em>cap</em>.
- Subjects
BACILLUS anthracis; BACILLUS (Bacteria); PLASMIDS; ANTHRAX; GENES
- Publication
Molecular Microbiology, 1997, Vol 23, Issue 6, p1229
- ISSN
0950-382X
- Publication type
Article
- DOI
10.1046/j.1365-2958.1997.3041667.x