Danese P N, Oliver G R, Barr K, Bowman G D, Rick P D, Silhavy T J
Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.
J Bacteriol. 1998 Nov;180(22):5875-84. doi: 10.1128/JB.180.22.5875-5884.1998.
In Escherichia coli, transcription of the degP locus, which encodes a heat-shock-inducible periplasmic protease, is controlled by two parallel signal transduction systems that each monitor extracytoplasmic protein physiology. For example, the heat-shock-inducible sigma factor, sigmaE, controls degP transcription in response to the overproduction and folded state of various extracytoplasmic proteins. Similarly, the CpxA/R two-component signal transduction system increases degP transcription in response to the overproduction of a variety of extracytoplasmic proteins. Since degP transcription is attuned to the physiology of extracytoplasmic proteins, we were interested in identifying negative transcriptional regulators of degP. To this end, we screened for null mutations that increased transcription from a strain containing a degP-lacZ reporter fusion. Through this approach, we identified null mutations in the wecE, rmlAECA, and wecF loci that increase degP transcription. Interestingly, each of these loci is responsible for synthesis of the enterobacterial common antigen (ECA), a glycolipid situated on the outer leaflet of the outer membrane of members of the family Enterobacteriaceae. However, these null mutations do not stimulate degP transcription by eliminating ECA biosynthesis. Rather, the wecE, rmlAECA, and wecF null mutations each impede the same step in ECA biosynthesis, and it is the accumulation of the ECA biosynthetic intermediate, lipid II, that causes the observed perturbations. For example, the lipid II-accumulating mutant strains each (i) confer upon E. coli a sensitivity to bile salts, (ii) confer a sensitivity to the synthesis of the outer membrane protein LamB, and (iii) stimulate both the Cpx pathway and sigmaE activity. These phenotypes suggest that the accumulation of lipid II perturbs the structure of the bacterial outer membrane. Furthermore, these results underscore the notion that although the Cpx and sigmaE systems function in parallel to regulate degP transcription, they can be simultaneously activated by the same perturbation.
在大肠杆菌中，编码热休克诱导型周质蛋白酶的degP基因座的转录由两个平行的信号转导系统控制，每个系统监测胞外蛋白的生理状态。例如，热休克诱导型σ因子σE响应各种胞外蛋白的过量产生和折叠状态来控制degP转录。同样，CpxA/R双组分信号转导系统响应各种胞外蛋白的过量产生而增加degP转录。由于degP转录与胞外蛋白的生理状态相协调，我们对鉴定degP的负转录调节因子感兴趣。为此，我们筛选了能增加含有degP-lacZ报告基因融合菌株转录的无效突变。通过这种方法，我们在wecE、rmlAECA和wecF基因座中鉴定到了能增加degP转录的无效突变。有趣的是，这些基因座中的每一个都负责肠杆菌共同抗原（ECA）的合成，ECA是一种位于肠杆菌科成员外膜外小叶上的糖脂。然而，这些无效突变并非通过消除ECA生物合成来刺激degP转录。相反，wecE、rmlAECA和wecF无效突变各自阻碍了ECA生物合成中的同一步骤，正是ECA生物合成中间体脂质II的积累导致了观察到的扰动。例如，每个积累脂质II的突变菌株（i）使大肠杆菌对胆盐敏感，（ii）对外膜蛋白LamB的合成敏感，（iii）刺激Cpx途径和σE活性。这些表型表明脂质II的积累扰乱了细菌外膜的结构。此外，这些结果强调了这样一个观点，即尽管Cpx和σE系统并行发挥作用来调节degP转录，但它们可以被相同的扰动同时激活。
