Lange R, Hengge-Aronis R
Department of Biology, University of Konstanz, Germany.
Genes Dev. 1994 Jul 1;8(13):1600-12. doi: 10.1101/gad.8.13.1600.
The second vegetative sigma factor sigma S (encoded by the rpoS gene) is the master regulator in a complex regulatory network that governs the expression of many stationary phase-induced and osmotically regulated genes in Escherichia coli. Using a combination of gene-fusion technology and quantitative immunoblot, pulse-labeling, and immunoprecipitation analyses, we demonstrate here that rpoS/sigma S expression is not only transcriptionally controlled, but is also extensively regulated at the levels of translation and protein stability. rpoS transcription is inversely correlated with growth rate and is negatively controlled by cAMP-CRP. In complex medium rpoS transcription is stimulated during entry into stationary phase, whereas in minimal media, it is not significantly induced. rpoS translation is stimulated during transition into stationary phase as well as by an increase in medium osmolarity. A model involving mRNA secondary structure is suggested for this novel type of post-transcriptional growth phase-dependent and osmotic regulation. Furthermore, sigma S is a highly unstable protein in exponentially growing cells (with a half-life of 1.4 min), that is stabilized at the onset of starvation. When cells are grown in minimal glucose medium, translational induction and sigma S stabilization occur in a temporal order with the former being stimulated already in late exponential phase and the latter taking place at the onset of starvation. Although sigma S does not control its own transcription, it is apparently indirectly involved in a negative feedback control that operates on the post-transcriptional level. Our analysis also indicates that at least five different signals [cAMP, a growth rate-related signal (ppGpp?), a cell density signal, an osmotic signal, and a starvation signal] are involved in the control of all these processes that regulate rpoS/sigma S expression.
第二种营养型σ因子σS（由rpoS基因编码）是一个复杂调控网络中的主要调节因子，该网络控制着大肠杆菌中许多稳定期诱导和渗透调节基因的表达。通过结合基因融合技术以及定量免疫印迹、脉冲标记和免疫沉淀分析，我们在此证明rpoS/σS的表达不仅受到转录控制，还在翻译和蛋白质稳定性水平上受到广泛调控。rpoS转录与生长速率呈负相关，并受到cAMP-CRP的负调控。在复合培养基中，rpoS转录在进入稳定期时受到刺激，而在基本培养基中，它没有明显诱导。rpoS翻译在进入稳定期以及培养基渗透压增加时受到刺激。针对这种新型的转录后生长阶段依赖性和渗透调节，提出了一个涉及mRNA二级结构的模型。此外，σS在指数生长的细胞中是一种高度不稳定的蛋白质（半衰期为1.4分钟），在饥饿开始时会稳定下来。当细胞在基本葡萄糖培养基中生长时，翻译诱导和σS稳定化按时间顺序发生，前者在指数后期已经受到刺激，后者在饥饿开始时发生。虽然σS不控制其自身转录，但它显然间接参与了在转录后水平上起作用的负反馈控制。我们的分析还表明，至少有五个不同的信号[cAMP、一个与生长速率相关的信号（ppGpp？）、一个细胞密度信号、一个渗透信号和一个饥饿信号]参与了所有这些调节rpoS/σS表达的过程的控制。
