Bellefontaine Anne-Flore, Pierreux Christophe E, Mertens Pascal, Vandenhaute Jean, Letesson Jean-Jacques, De Bolle Xavier
Unité de Recherche en Biologie Moléculaire (URBM), Facultés Universitaires Notre Dame de la Paix, 61, rue de Bruxelles, B-5000 Namur, Belgium.
Mol Microbiol. 2002 Feb;43(4):945-60. doi: 10.1046/j.1365-2958.2002.02777.x.
CtrA is a master response regulator found in many alpha-proteobacteria. In Caulobacter crescentus and Sinorhizobium meliloti, this regulator is essential for viability and is transcriptionally autoregulated. In C. crescentus, it is required for the regulation of multiple cell cycle events, such as DNA methylation, DNA replication, flagella and pili biogenesis and septation. Here, we report the characterization of the ctrA gene homologue in the alpha2-proteobacteria Brucella abortus, a facultative intracellular pathogen responsible for brucellosis. We detected CtrA expression in the main Brucella species, and its overproduction led to a phenotype typical of cell division defect, consistent with its expected role. A purified B. abortus CtrA recombinant protein (His6-CtrA) was shown to protect the B. abortus ctrA promoter from DNase I digestion, suggesting transcriptional autoregulation, and this protection was enhanced under CtrA phosphorylation on a conserved Asp residue. Despite the similarities shared by B. abortus and C. crescentus ctrA, the pathway downstream from CtrA may be distinct, at least partially, in both bacteria. Indeed, beside ctrA itself, only one (the ccrM gene) out of four B. abortus homologues of known C. crescentus CtrA targets is bound in vitro by phosphorylated B. abortus CtrA. Moreover, further footprinting experiments support the hypothesis that, in B. abortus, CtrA might directly regulate the expression of the rpoD, pleC, minC and ftsE homologues. Taken together, these results suggest that, in B. abortus and C. crescentus, similar cellular processes are regulated by CtrA through the control of distinct target genes. The plasticity of the regulation network involving CtrA in these two bacteria may be related to their distinct lifestyles.
CtrA是在许多α-变形菌中发现的主要应答调节因子。在新月柄杆菌和苜蓿中华根瘤菌中，这种调节因子对于生存能力至关重要，并且受到转录自调控。在新月柄杆菌中，它是调控多个细胞周期事件所必需的，如DNA甲基化、DNA复制、鞭毛和菌毛的生物合成以及细胞分裂。在此，我们报道了α2-变形菌流产布鲁氏菌中ctrA基因同源物的特性，流产布鲁氏菌是一种导致布鲁氏菌病的兼性胞内病原体。我们在主要的布鲁氏菌种中检测到了CtrA的表达，其过量表达导致了典型的细胞分裂缺陷表型，这与其预期作用一致。纯化的流产布鲁氏菌CtrA重组蛋白（His6-CtrA）能够保护流产布鲁氏菌ctrA启动子免受DNase I消化，表明存在转录自调控，并且在保守的天冬氨酸残基上CtrA磷酸化时这种保护作用增强。尽管流产布鲁氏菌和新月柄杆菌的ctrA有相似之处，但在这两种细菌中，CtrA下游的途径可能至少部分不同。实际上，除了ctrA自身外，已知的新月柄杆菌CtrA靶点的四个流产布鲁氏菌同源物中只有一个（ccrM基因）在体外能被磷酸化的流产布鲁氏菌CtrA结合。此外，进一步的足迹实验支持这样的假说：在流产布鲁氏菌中，CtrA可能直接调控rpoD、pleC、minC和ftsE同源物的表达。综上所述，这些结果表明，在流产布鲁氏菌和新月柄杆菌中，相似的细胞过程通过对不同靶基因的控制由CtrA进行调控。这两种细菌中涉及CtrA的调控网络的可塑性可能与它们不同的生活方式有关。
