Regulation of Stationary Phase in Escherichia coli

描述(申请人提供)：当营养耗尽或分泌的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，细菌生命周期的这一静止阶段可以通过饥饿一种基本的营养物质来实现，例如碳源、磷酸盐或氨形式的氮。静止期发育计划的实施需要交替的西格玛因子RpoS。在此之前，我们已经确定了一个孤儿反应调节因子SprE(也称为RSSB或MviA)。在快速生长的细胞中，SprE引导rpos被依赖于ATP的蛋白酶CIPP/X破坏，从而将这个sigma因子维持在低水平。当细胞缺乏碳时，SprE活性受到抑制，rpos水平迅速上升。我们还发现RPOS可以刺激SprE的表达。矛盾的是，这种调节反馈环路导致在蛋白质可能不活跃的情况下，在静止期细胞中产生高水平的SprE。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，并探索其功能意义或这种调控反馈回路。我们还将确定当细胞缺乏磷酸盐或氨时，负责形成静止相的信号转导机制，并确定当细胞仅缺乏这些元素中的一种时，细胞如何整合可能产生的相互冲突的信号。固定相提出了几个至关重要的问题。细胞感觉到即将到来的饥饿，并对此做出反应。当所有其他基本营养素都充足时，他们怎么知道他们即将耗尽一种基本营养素的媒介？相互冲突的信号是如何整合的？最后，由于RPOS对几种细菌的发病机制很重要，了解这个复杂的信号转导网络可能会揭示这些病原体的盔甲中的裂缝。

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.