Estacio W, Anna-Arriola S S, Adedipe M, Márquez-Magaña L M
Department of Biology, San Francisco State University, San Francisco, California 94132, USA.
J Bacteriol. 1998 Jul;180(14):3548-55. doi: 10.1128/JB.180.14.3548-3555.1998.
The fla/che region contains more than 30 genes required for flagellar synthesis and chemotaxis in Bacillus subtilis, including the gene for the flagellum-specific sigmaD factor, sigD. Sequence and primer extension data demonstrate that a PA promoter immediately upstream of flgB, henceforth referred to as the fla/che PA, and the PD-3 promoter are active in vivo. Transcription from the PD-3 element is dependent on sigmaD activity and is regulated by the flagellum-specific negative regulator, FlgM. In a strain containing a deletion of fla/che PA (PADelta), sigmaD protein was not detected, demonstrating that the fla/che PA is necessary for wild-type expression of the sigD gene. Thus, sigD is part of the >26-kb fla/che operon. Consistent with a lack of detectable sigmaD protein, the PADelta strain grows as long filaments and does not express a sigmaD-dependent hag::lacZ reporter construct. These phenotypes are indicative of a lack of sigD expression or complete inhibition of sigmaD activity by FlgM. However, sigmaD activity is found in a double mutant containing the PADelta and a null mutation in flgM. The double mutant no longer grows as long filaments, and expression of hag::lacZ is partially restored. These data demonstrate that a low level of sigmaD activity does exist in the PADelta mutant but can be detected only in the presence of a null mutation in flgM. Therefore, normal expression of sigD may also involve another promoter(s) within the fla/che operon.
枯草芽孢杆菌的fla/che区域包含30多个鞭毛合成和趋化作用所需的基因，包括鞭毛特异性σD因子sigD的基因。序列和引物延伸数据表明，flgB上游紧邻的一个PA启动子（此后称为fla/che PA）和PD - 3启动子在体内具有活性。来自PD - 3元件的转录依赖于σD活性，并受鞭毛特异性负调控因子FlgM的调节。在一个缺失fla/che PA（PADelta）的菌株中，未检测到σD蛋白，这表明fla/che PA对于sigD基因的野生型表达是必需的。因此，sigD是>26 kb的fla/che操纵子的一部分。与未检测到可检测的σD蛋白一致，PADelta菌株长成细长丝，并且不表达依赖于σD的hag::lacZ报告构建体。这些表型表明缺乏sigD表达或FlgM对σD活性的完全抑制。然而，在同时含有PADelta和flgM无效突变的双突变体中发现了σD活性。该双突变体不再长成细长丝，并且hag::lacZ的表达部分恢复。这些数据表明，在PADelta突变体中确实存在低水平的σD活性，但只有在flgM无效突变存在的情况下才能检测到。因此，sigD的正常表达可能还涉及fla/che操纵子内的另一个启动子。
