1887

Abstract

A two-component regulatory system, , plays an important role in the pH-dependent regulation of , a global activator for virulence determinants including invasion genes, in . The authors examined whether the homologues have some function in the expression of serovar Typhimurium invasion genes via the regulation of , an activator for these genes. In a mutant, the expression level was reduced to less than 10 % of that in the parent strain at pH 6·0. This mutant strain also showed undetectable synthesis of an invasion gene product, SipC, at pH 6·0 and reduced cell invasion capacity – as low as 20 % of that of the parent. In this mutant, the reduction in expression was much less marked at pH 8·0 than at pH 6·0 – no less than 50 % of that in the parent, and no significant reduction was observed in either SipC synthesis or cell invasion rate, compared to the parent. Unexpectedly, a mutant strain and the parent showed no apparent difference in all three characteristics described above at either pH. These results indicate that in , the sensor kinase CpxA activates , and consequently, invasion genes and cell invasion capacity at pH 6·0. At pH 8·0, however, CpxA does not seem to have a large role in activation of these factors. Further, the results show that this CpxA-mediated activation does not require its putative cognate response regulator, CpxR. This suggests that CpxA may interact with regulator(s) other than CpxR to achieve activation at low pH.

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2003-10-01
2019-11-14
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