SENSORY TRANSDUCTION IN BACTERIAL CHEMOTAXIS

能动细菌具有一个刺激-反应系统， 输入是化学引诱剂的局部浓度， 输出是细胞的运动。 在大肠杆菌中， 是由一些特定受体的占有率决定的， 而输出是由大约 六根鞭毛丝 当纤维反向转动时- 顺时针方向，细胞稳定地沿着平滑的路径游动（它运行）; 当它们顺时针旋转时，细胞以高度不稳定的方式运动， 净位移小的方式（翻滚）。 一般来说， 这些模式交替，细胞执行三维 随机游走 在过去的一秒钟里，受体的占有率是 与前三个月相比， 秒，并且细胞对差异做出响应：运行是 将细胞带向有利的方向。 的 目前的研究集中在分子事件，耦合 鞭毛的受体，即，所需的事件 趋化性信号 已知有四种基因产物 CheW，CheA，CheY和CheZ CheY似乎是第二个 信使由受体激活并扩散到 鞭毛，在那里它增强顺时针旋转（翻滚）。 来自体外研究的证据表明， 磷酸化的结果，由CheA催化。 但在 在体内，在不存在CheA的情况下， 添加乙酸盐，通过一种似乎涉及 乙酰辅酶A合成酶 重组实验将是 在删除了大多数趋化基因的细胞中进行， 确定用于CheW、CheA 和CheY，并了解更多关于相互作用的动力学 CheY CheZ和鞭毛开关 行为反应将 在拴系细胞测定中进行监测。 acs基因将会 克隆、测序及基因产物鉴定。 证据 用于与其他组件的交互将由各种 方法，包括体外寻找乙酰化或 腺苷酸化 将开发一种体外运动试验， 将允许快速比较对切换的影响， 纯化的细胞质成分。 用于判断运动性的测定 并且细胞群体的趋化性将得到改善。 最后， 将分析系留微单元的旋转行为， 确定电机运行时的相关开关统计数据， 高速度 这将有助于我们了解 同一细胞上不同鞭毛的同步化， 更准确的预测游泳行为的基础上， 栓系细胞测定的结果。 长期目标是 在感觉传导的分子水平上的描述， 细菌趋化性

Motile bacteria possess a stimulus-response system in which the input is the local concentration of a chemical attractant and the output is the motion of the cell. In Escherichia coli, the input is determined by the occupancy of a number of specific receptors, while the output is determined by the sense of rotation of about six flagellar filaments. When the filaments turn counter- clockwise, the cell swims steadily along a smooth path (it runs); when they turn clockwise, the cell moves in a highly erratic manner with little net displacement (it tumbles). Normally, these modes alternate, and the cell executes a three-dimensional random walk. The receptor occupancy over the past second is compared to the receptor occupancy over the previous three seconds, and the cell responds to the difference: runs are extended that carry the cell in a favorable direction. The present research focuses on the molecular events that couple the receptors to the flagella, i.e., the events required for chemotactic signaling. Four gene products are known to be involved, CheW, CheA, CheY and CheZ. CheY appears to be a second messenger that is activated by the receptors and diffuses to the flagella, where it enhances clockwise rotation (tumbles). Evidence from in vitro studies suggests that this activation results from phosphorylation, catalyzed by CheA. However, in vivo, CheY can be activated in the absence of CheA following the addition of acetate, via a pathway that appears to involve acetyl-CoA synthetase. Reconstitution experiments will be carried out in cells deleted for most of the chemotaxis genes to determine optimum stoichiometries for signaling for CheW, CheA and CheY, and to learn more about the kinetics of interaction of CheY, CheZ and the flagellar switch. Behavioral responses will be monitored in a tethered-cell assay. The acs gene will be clone and sequenced and its gene product characterized. Evidence for interaction with other components will be sought by a variety of means, including an in vitro search for acetylation or adenylylation. An in vitro motor assay will be developed that will allow rapid comparisons of the effects on switching of purified cytoplasmic components. Assays for judging the motility and chemotaxis of cell populations will be improved. Finally, the rotational behavior of tethered minicells will be analyzed to determine the switching statistics relevant when motors run at high speed. This will improve our understanding of the synchronization of different flagella on the same cell and allow more accurate predictions of swimming behavior based on the results of tethered-cell assays. The long-range goal is a description at the molecular level of sensory transduction in bacterial chemotaxis.