Loewen P C, Hu B, Strutinsky J, Sparling R
Department of Microbiology, University of Manitoba, Winnipeg, Canada.
Can J Microbiol. 1998 Aug;44(8):707-17. doi: 10.1139/cjm-44-8-707.
In Escherichia coli, the transcription factor sigma s, encoded by rpoS, controls the expression of a large number of genes involved in cellular responses to a diverse number of stresses, including starvation, osmotic stress, acid shock, cold shock, heat shock, oxidative DNA damage, and transition to stationary phase. A list of over 50 genes under the control of rpoS has been compiled. The transcription factor sigma s acts predominantly as a positive effector, but it does have a negative effect on some genes. The synthesis and accumulation of sigma s are controlled by mechanisms affecting transcription, translation, proteolysis, and the formation of the holoenzyme complex. Transcriptional control of rpoS involves guanosine 3',5'-bispyrophosphate (ppGpp) and polyphosphate as positive regulators and the cAMP receptor protein-cAMP complex (CRP-cAMP) as a negative regulator. Translation of rpoS mRNA is controlled by a cascade of interacting factors, including Hfq, H-NS, dsrA RNA, LeuO, and oxyS RNA that seem to modulate the stability of a region of secondary structure in the ribosome-binding region of the gene's mRNA. The transcription factor sigma s is sensitive to proteolysis by ClpPX in a reaction that is promoted by RssB and inhibited by the chaperone DnaK. Despite the demonstrated involvement of so many factors, arguments have been presented suggesting that sensitivity to proteolysis may be the single most important modulator of sigma s levels. The activity of sigma s may also be modulated by trehalose and glutamate, which activate holoenzyme formation and promote holoenzyme binding to certain promoters.
在大肠杆菌中，由rpoS编码的转录因子σS控制着大量参与细胞对多种应激反应的基因的表达，这些应激包括饥饿、渗透应激、酸休克、冷休克、热休克、氧化性DNA损伤以及向稳定期的转变。一份受rpoS控制的50多个基因的清单已被整理出来。转录因子σS主要作为一种正效应物起作用，但它对某些基因也有负效应。σS的合成和积累受影响转录、翻译、蛋白水解以及全酶复合物形成的机制控制。rpoS的转录控制涉及鸟苷3',5'-双焦磷酸（ppGpp）和多聚磷酸盐作为正调节因子，以及环腺苷酸受体蛋白 - 环腺苷酸复合物（CRP - cAMP）作为负调节因子。rpoS mRNA的翻译受一系列相互作用因子的控制，包括Hfq、H - NS、dsrA RNA、LeuO和oxyS RNA，这些因子似乎调节该基因mRNA核糖体结合区域二级结构区域的稳定性。转录因子σS对ClpPX介导的蛋白水解敏感，该反应由RssB促进并受伴侣蛋白DnaK抑制。尽管已证明有如此多的因子参与其中，但有人提出，对蛋白水解的敏感性可能是σS水平最重要的单一调节因素。σS的活性也可能受到海藻糖和谷氨酸的调节，它们可激活全酶形成并促进全酶与某些启动子的结合。
