Regulation of Stationary Phase in Escherichia coli

描述（由申请人提供）：当营养物质耗尽或分泌废物积累到高水平时，大肠杆菌停止生长。在这些条件下，细菌启动了一个复杂的发育计划，以延长生存时间。在实验室中，细菌生命周期的这个固定阶段可以通过饥饿来实现，如碳源、磷酸盐或氨形式的氮。固定阶段开发计划的实施需要备用σ因子rpo。之前我们已经确定了孤儿反应调节剂SprE（也称为RssB或MviA）。在快速生长的细胞中，SprE引导RpoS被atp依赖的蛋白酶CIpP/X破坏，从而将该sigma因子维持在低水平。当细胞缺乏碳时，SprE活性被抑制，RpoS水平迅速上升。我们还发现RpoS刺激了sprE的表达。矛盾的是，这种调节反馈回路导致固定期细胞中高水平的SprE，而该蛋白可能是无活性的。利用遗传学和生物化学的结合，我们将定义控制SprE活性的信号转导途径，我们将探索这种调节反馈回路的功能意义。我们还将确定当细胞缺乏磷酸盐或氨时负责固定期发展的信号转导机制，我们将确定细胞如何整合当细胞仅缺乏其中一种元素时可能出现的冲突信号。定相提出了几个重要的基本问题。细胞感知并对即将到来的饥饿做出反应。当所有其他必需营养素都很丰富时，他们怎么知道他们即将耗尽一种必需营养素的媒介？如何整合相互冲突的信号？最后，由于RpoS对几种细菌的发病机制很重要，对这种复杂信号转导网络的理解可能会揭示这些病原体盔甲上的裂缝。

DESCRIPTION (provided by applicant): Growth of Escherichia coli ceases when nutrients are depleted or when secreted waste products accumulate to high levels. Under these conditions the bacteria initiate a complex developmental plan to allow extended survival. In the lab this stationary phase of the bacterial life cycle can be achieved by starvation for a single essential nutrient such as a carbon source, phosphate, or nitrogen in the form of ammonia. Implementation of the stationary phase developmental plan requires the alternate sigma factor RpoS.Previously we have identified an orphan response regulator SprE (also known as RssB or MviA). In rapidly growing cells, SprE directs RpoS for destruction by the ATP-dependent protease CIpP/X, thus maintaining this sigma factor at low levels. SprE activity is inhibited when cells are starved for carbon, and RpoS levels quickly rise. We have also shown that RpoS stimulates sprE expression. Paradoxically this regulatory feedback loop results in high levels of SprE in stationary phase cells when the protein is presumably inactive. Using a combination of genetics and biochemistry we will define the signal transduction pathway that controls SprE activity, and we will probe the functional significance or this regulatory feedback loop. We will also determine the signal transduction mechanisms responsible for the development of stationary phase when cells are starved for phosphate or ammonia, and we will determine how cells integrate the conflicting signals that can arise when cells are starved for only one of these elements. Stationary phase raises several questions of fundamental importance. Cells sense and respond to impending starvation. How do they know they are about to deplete the medium of one essential nutrient when all other essential nutrients are abundant? How are conflicting signals integrated? Finally, since RpoS is important for the pathogenesis of several bacteria, an understanding of this complex signal transduction network may reveal chinks in the armor of these pathogens.