New family of regulators in the environmental signaling pathway which activates the general stress transcription factor σB of Bacillus subtilis
New family of regulators in the environmental signaling pathway which activates the general stress transcription factor σB of Bacillus subtilis
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DOI：
10.1128/jb.183.4.1329-1338.2001
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发表时间：
2001-02-01
影响因子：
3.2
通讯作者：
Price, CW
中科院分区：
文献类型：
--
作者：
Akbar, S;Gaidenko, TA;Price, CW
枯草芽孢杆菌（Bacillus subtilis）的一般胁迫调控由备选转录因子sigma (B)控制，当细胞遇到生长限制能量或环境胁迫时，该转录因子被激活。RsbT丝氨酸-苏氨酸激酶需要将环境胁迫信号传递给sigma (B)，这种激酶活性在体外被RsbR蛋白放大，RsbR蛋白是一种积极的调节因子，对体内对盐或热应激的全面反应很重要。先前的遗传分析表明，RsbR的功能与其他未识别的调控因子是冗余的。对翻译的枯草芽孢杆菌基因组的搜索发现了6个与RsbR有显著相似的同源蛋白：YetI、YezB、YkoB、YojH、YqhA和YtvA。使用三种不同的方法研究了它们可能的调节作用。首先，遗传分析发现，6个旁系基因中有4个的零突变对sigma (B)环境信号通路有明显的影响，无论是单独的还是联合的。两个例外是yetI和yezB，这两个相邻的基因似乎编码了一个分裂平行体。其次，生化分析发现YkoB、YojH和YqhA在体外被RsbT环境信号激酶特异性磷酸化，正如之前的研究显示的那样，RsbR在其c端区域的两个苏氨酸残基上被磷酸化。这两个残基在三个磷酸化的类似物中都是保守的，但在非rbt底物中不存在：YetI和YezB，每个只含有一个保守残基；YtvA缺乏这两个残基，而是具有n端PAS结构域。第三，对酵母双杂交系统的分析表明，这六种亲缘物相互作用，并与RsbR和RsbS环境调节因子相互作用。我们的数据表明(i) RsbR、YkoB、YojH、YqhA和YtvA在环境胁迫信号通路中起作用；YtvA起到积极调节作用；（iii） RsbR、YkoB、YojH和YqhA共同作为有效的负调节因子，其缺失使非应激细胞中的sigma (B)活性增加400倍以上。
Expression of the general stress regulon of Bacillus subtilis is controlled by the alternative transcription factor sigma (B), which is activated when cells encounter growth-limiting energy or environmental stresses. The RsbT serine-threonine kinase is required to convey environmental stress signals to sigma (B), and this kinase activity is magnified in vitro by the RsbR protein, a positive regulator important for full in vivo response to salt or heat stress. Previous genetic analysis suggested that RsbR function is redundant with other unidentified regulators. A search of the translated B. subtilis genome found six paralogous proteins with significant similarity to RsbR: YetI, YezB, YkoB, YojH, YqhA, and YtvA. Their possible regulatory roles were investigated using three different approaches. First, genetic analysis found that null mutations in four of the six paralogous genes have marked effects on the sigma (B) environmental signaling pathway, either singly or in combination. The two exceptions were yetI and yezB, adjacent genes which appear to encode a split paralog. Second, biochemical analysis found that YkoB, YojH, and YqhA are specifically phosphorylated in vitro by the RsbT environmental signaling kinase, as had been previously shown for RsbR, which is phosphorylated on two threonine residues in its C-terminal region. Both residues are conserved in the three phosphorylated paralogs but are absent in the ones that were not substrates of RsbT: YetI and YezB, each of which bears only one of the conserved residues; and YtvA, which lacks both residues and instead possesses an N-terminal PAS domain. Third, analysis in the yeast two-hybrid system suggested that all six paralogs interact with each other and with the RsbR and RsbS environmental regulators. Our data indicate that (i) RsbR, YkoB, YojH, YqhA, and YtvA function in the environmental stress signaling pathway; (ii) YtvA acts as a positive regulator; and (iii) RsbR, YkoB, YojH, and YqhA collectively act as potent negative regulators whose loss increases sigma (B) activity more than 400-fold in unstressed cells.