Deuerling E, Mogk A, Richter C, Purucker M, Schumann W
Institute of Genetics, University of Bayreuth, Germany.
Mol Microbiol. 1997 Mar;23(5):921-33. doi: 10.1046/j.1365-2958.1997.2721636.x.
The ftsH gene of Bacillus subtilis has been identified as a general stress gene which is transiently induced after thermal or osmotic upshift. The FtsH protein exhibits 70.1% homology to FtsH of Escherichia coli which constitutes an essential ATP- and Zn(2+)-dependent protease anchored in the cytoplasmic membrane via two N-terminal transmembrane domains. This paper describes the isolation and functional characterization of an ftsH null mutant which was obtained by integration of a cat-cassette near the 5' end of ftsH, thereby preventing the synthesis of FtsH protein. In contrast to the situation in E. coli, ftsH is dispensable in B. subtilis but results in a pleiotropic phenotype. While the mutant cells grew mostly as large filaments under physiological conditions, they turned out to be extremely sensitive to heat and salt stress. Although ftsH is necessary for adaptation to heat, it is not involved in the regulation of the heat-shock response. The induction profiles of representative genes of the CIRCE and sigma-B regulon and class III heat-shock genes ion and clpC were identical in the wild type and the ftsH null mutant. Furthermore, the ftsH knockout strain was unable to sporulate, and this failure was probably due to the absence of Spo0A protein which is essential for entry into the sporulation programme. In addition, secretion of bulk exoproteins was severely impaired in the ftsH null mutant after entry into stationary phase. The alpha-amylase and subtilisin activity in the supernatant was specifically tested. Whereas the activity of alpha-amylase increased after entry into stationary phase in both the wild type and the ftsH mutant strain, that of subtilisin encoded by aprE was prevented at the level of transcription in the mutant. Most of these results can be explained by the failure to synthesize appropriate amounts of Spo0A protein in the ftsH null mutant and point to ftsH as a developmental checkpoint.
枯草芽孢杆菌的ftsH基因已被鉴定为一种一般应激基因，在热应激或渗透压升高后会短暂诱导表达。FtsH蛋白与大肠杆菌的FtsH具有70.1%的同源性，大肠杆菌的FtsH是一种必需的、依赖ATP和Zn(2+)的蛋白酶，通过两个N端跨膜结构域锚定在细胞质膜上。本文描述了一个ftsH缺失突变体的分离和功能特性，该突变体是通过在ftsH的5'端附近整合一个cat盒获得的，从而阻止了FtsH蛋白的合成。与大肠杆菌的情况不同，ftsH在枯草芽孢杆菌中是可有可无的，但会导致多效性表型。虽然突变细胞在生理条件下大多长成大的丝状体，但它们对热和盐胁迫极其敏感。尽管ftsH对于适应热是必需的，但它不参与热休克反应的调控。CIRCE和sigma-B调节子以及III类热休克基因ion和clpC的代表性基因的诱导谱在野生型和ftsH缺失突变体中是相同的。此外，ftsH敲除菌株无法形成芽孢，这种失败可能是由于缺乏进入芽孢形成程序所必需的Spo0A蛋白。另外，进入稳定期后，ftsH缺失突变体中大量外分泌蛋白的分泌严重受损。对上清液中的α-淀粉酶和枯草杆菌蛋白酶活性进行了特异性检测。虽然野生型和ftsH突变菌株进入稳定期后α-淀粉酶活性均增加，但突变体中由aprE编码的枯草杆菌蛋白酶活性在转录水平受到抑制。这些结果大多可以通过ftsH缺失突变体中无法合成适量的Spo0A蛋白来解释，这表明ftsH是一个发育检查点。
