Mecsas J, Rouviere P E, Erickson J W, Donohue T J, Gross C A
Department of Bacteriology, University of Wisconsin-Madison 53706.
Genes Dev. 1993 Dec;7(12B):2618-28. doi: 10.1101/gad.7.12b.2618.
sigma E and sigma 32 are two heat- and ethanol-inducible sigma-factors in Escherichia coli. The sigma 32 regulon is also induced by unfolded and misfolded proteins in the cytoplasm, and the function of many of the proteins in the sigma 32 regulon is to bind to cytoplasmic proteins and assist them in folding or unfolding. To further understand the function of the sigma E regulon, we searched for mutants that affected sigma E activity. Our results indicate that a signal generated by expression of outer membrane proteins modulates sigma E activity. Specifically, sigma E activity is induced by increased expression of OMPs and is reduced by decreased expression of OMPs. In addition, mutations that cause misfolded OMPs induce sigma E activity. This signal is generated after the fate of OMPs and periplasmic proteins diverge in the secretory pathway and is not the result of an accumulation of OMP precursors in the cytoplasm. Our results indicate that this effect of OMPs is specific to the sigma E regulon, because none of the above mutations affect sigma 32 activity. We propose that the sigma E regulon is involved in processes that occur in extracytoplasmic compartments and that these two heat-inducible regulons may have distinct but complementary roles of monitoring the state of proteins in the cytoplasm (sigma 32) and outer membrane (sigma E).
σE和σ32是大肠杆菌中两种受热和乙醇诱导的σ因子。σ32调控子也可由细胞质中未折叠和错误折叠的蛋白质诱导，并且σ32调控子中的许多蛋白质的功能是与细胞质蛋白质结合并协助它们折叠或展开。为了进一步了解σE调控子的功能，我们筛选了影响σE活性的突变体。我们的结果表明，外膜蛋白表达产生的信号调节σE活性。具体而言，σE活性由外膜蛋白表达增加诱导，并由外膜蛋白表达降低而降低。此外，导致外膜蛋白错误折叠的突变会诱导σE活性。这个信号是在分泌途径中外膜蛋白和周质蛋白的命运分化之后产生的，而不是细胞质中外膜蛋白前体积累的结果。我们的结果表明，外膜蛋白的这种作用对σE调控子具有特异性，因为上述任何突变均不影响σ32活性。我们提出，σE调控子参与胞外区室中发生的过程，并且这两个受热诱导的调控子可能在监测细胞质（σ32）和外膜（σE）中蛋白质状态方面具有不同但互补的作用。
