科研之友
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摘要
DksA acts as a co-factor for the intracellular small signalling molecule ppGpp during the stringent response. We recently reported that the expression of the haemagglutinin protease (HAP), which is needed for shedding of the cholera pathogen Vibrio cholerae during the late phase of infection, is significantly downregulated in V. cholerae Delta dksA mutant (Delta dksA(vc)) cells. So far, it has been shown that HAP production by V. cholerae cells is critically regulated by HapR and also by RpoS. Here, we provide evidence that V. cholerae DksA (DksA(vc)) positively regulates HapR at both the transcriptional and post-transcriptional levels. We show that in Delta dksA(vc), cells the CsrB/C/D sRNAs, required for the maintenance of intracellular levels of hapR transcripts during the stationary growth, are distinctly downregulated. Moreover, the expression of exponential phase regulatory protein Fis, a known negative regulator of HapR, was found to continue even during the stationary phase in Delta dksA(vc) cells compared to that of wild-type strain, suggesting another layer of complex regulation of HapR by DksA(vc). Extensive reporter construct-based and quantitative reverse-transcriptase PCR (qRT-PCR) analyses supported that RpoS is distinctly downregulated at the post-transcriptional/translational levels in stationary phase-grown Delta dksA(vc) cells. Since HAP expression through HapR and RpoS is stationary phase-specific in V. cholerae, it appears that DksA(vc) is also a critical stationary phase regulator for fine tuning of the expression of HAP. Moreover, experimental evidence provided in this study clearly supports that DksA(vc) is sitting at the top of the hierarchy of regulation of expression of HAP in V. cholerae.
- 出版日期2017-6
