Huang X, Helmann J D
Section of Microbiology, Cornell University, Ithaca, NY 14853-8101, USA.
J Mol Biol. 1998 May 29;279(1):165-73. doi: 10.1006/jmbi.1998.1765.
The promoter selectivity of RNA polymerase (RNAP) can be altered by the association with alternative sigma subunits. Bacillus subtilis hosts a multitude of sigma factors, several of which coordinate the complex developmental program culminating in endospore formation. Genome sequencing has revealed an unanticipated seven new sigma factors of the highly divergent extracytoplasmic function (ECF) sub-family. Virtually nothing is known regarding either the promoter selectivity or the target genes for these newly identified sigma factors. We have used saturation mutagenesis to define a promoter consensus for recognition by one such ECF sigma factor, sigma X. The resulting consensus sequence was used to identify candidate sigma X target sites. Three newly identified sigma X-dependent promoters precede genes encoding regulatory proteins: an AbrB homolog (Abh), a putative response regulator aspartate phosphatase (RapD), and a regulator of autolysin expression (LytR). sigma X also contributes to the expression of CsbB, a putative membrane-bound glucosyl transferase that is partially controlled by the sigma B stress response sigma factor. Since LytR modulates the expression of the major autolytic amidase and CsbB may function in peptidoglycan synthesis or modification, we suggest that sigma X participates in the regulation of peptidoglycan synthesis and turnover.
RNA聚合酶（RNAP）与替代的σ亚基结合可改变其启动子选择性。枯草芽孢杆菌拥有多种σ因子，其中一些因子协调复杂的发育程序，最终形成芽孢。基因组测序揭示了高度不同的胞外功能（ECF）亚家族中七个意外的新σ因子。对于这些新鉴定的σ因子的启动子选择性或靶基因几乎一无所知。我们利用饱和诱变来确定一种这样的ECF σ因子σX识别的启动子共有序列。所得的共有序列用于鉴定候选的σX靶位点。三个新鉴定的依赖于σX的启动子位于编码调节蛋白的基因之前：一个AbrB同源物（Abh）、一个假定的应答调节天冬氨酸磷酸酶（RapD）和一个自溶素表达调节因子（LytR）。σX也有助于CsbB的表达，CsbB是一种假定的膜结合葡糖基转移酶，部分受σB应激反应σ因子控制。由于LytR调节主要自溶酰胺酶表达，且CsbB可能在肽聚糖合成或修饰中起作用，我们认为σX参与肽聚糖合成和周转的调节。
