Márquez L M, Helmann J D, Ferrari E, Parker H M, Ordal G W, Chamberlin M J
Department of Biochemistry, University of California, Berkeley 94720.
J Bacteriol. 1990 Jun;172(6):3435-43. doi: 10.1128/jb.172.6.3435-3443.1990.
Gene expression in Bacillus subtilis can be controlled by alternative forms of RNA polymerase programmed by distinct sigma factors. One such factor, sigma D (sigma 28), is expressed during vegetative growth and has been implicated in the transcription of a regulon of genes expressed during exponential growth and the early stationary phase. We have studied several functions related to flagellar synthesis and chemotaxis in B. subtilis strains in which sigma D is missing or is present at reduced levels. Previous studies showed that a null mutant, which contains a disrupted copy of the sigma D structural gene (sigD), fails to synthesize flagellin and grows as long filaments. We now show that these defects are accompanied by the lack of synthesis of the methyl-accepting chemotaxis proteins and a substantial decrease in two autolysin activities implicated in cell separation. A strain containing an insertion upstream of the sigD gene that reduces the level of sigma D protein grew as short chains and was flagellated but was impaired in chemotaxis and/or motility. This reduced level of sigma D expression suggests that the sigD gene may be part of an operon. A strain containing an insertion downstream of the sigD gene expressed nearly wild-type levels of sigma D protein but was also impaired in chemotaxis and/or motility, suggesting that genes downstream of sigD may also be involved in these functions. Genetic experiments demonstrate that sigD is allelic to the flaB locus, which was initially isolated as a locus affecting flagellin expression (G. F. Grant and M. I. Simon, J. Bacteriol. 99:116-124, 1969).
枯草芽孢杆菌中的基因表达可由由不同的sigma因子编程的RNA聚合酶的替代形式控制。其中一个这样的因子，sigma D（sigma 28），在营养生长期间表达，并且与指数生长和早期稳定期表达的一组基因的转录有关。我们研究了sigma D缺失或水平降低的枯草芽孢杆菌菌株中与鞭毛合成和趋化性相关的几种功能。先前的研究表明，一个无效突变体，其包含sigma D结构基因（sigD）的破坏拷贝，不能合成鞭毛蛋白并长成细丝。我们现在表明，这些缺陷伴随着甲基接受趋化蛋白合成的缺乏以及与细胞分离有关的两种自溶素活性的大幅降低。一个在sigD基因上游含有插入片段从而降低sigma D蛋白水平的菌株长成短链并且有鞭毛，但在趋化性和/或运动性方面受损。这种降低的sigma D表达水平表明sigD基因可能是一个操纵子的一部分。一个在sigD基因下游含有插入片段且表达接近野生型水平的sigma D蛋白的菌株在趋化性和/或运动性方面也受损，这表明sigD下游的基因也可能参与这些功能。遗传实验证明sigD与flaB位点等位，flaB位点最初是作为一个影响鞭毛蛋白表达的位点分离出来的（G.F.格兰特和M.I.西蒙，《细菌学杂志》第99卷：116 - 124页，1969年）。
