SENSORY TRANSDUCTION IN BACTERIAL CHEMOTAXIS

游动细菌拥有一种刺激反应系统，在该系统中 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，输入 是由许多特定受体的占有率决定的， 而输出是由大约 六根鞭毛细丝。当细丝反转时- 顺时针方向，细胞沿着一条平坦的路径稳定地游着(它跑)； 当它们顺时针旋转时，细胞以非常不规律的方式运动 以净位移很小的方式(它翻滚)。通常， 这两种模式交替使用，细胞执行三维 随机游走。过去一秒的接收器占有率为 与前三年的受体占有率相比 秒，细胞对差异做出响应：运行是 将细胞带向有利方向的延伸。这个 目前的研究主要集中在连接两个分子的分子事件 鞭毛的受体，即所需的事件 趋化信号。已知的四种基因产物是 涉及，咀嚼，切和切。Chey似乎是第二个 由受体激活并扩散到 鞭毛，在那里它加强顺时针旋转(翻滚)。 来自体外研究的证据表明，这种激活 由CHEA催化的磷酸化的结果。但是，在 Vivo，Chey可以在没有Chea的情况下激活 醋酸盐的添加，通过一条似乎涉及 乙酰辅酶A合成酶。重建实验将是 在缺失了大部分趋化基因的细胞中进行 确定信号传递的最佳化学计量比 和Chey，并进一步了解相互作用的动力学。 切伊，切兹和鞭毛开关。行为反应将 在系留细胞检测中被监测。ACS基因将是 克隆测序并对其基因产物进行鉴定。证据 对于与其他组件的交互，将由各种不同的 方法，包括体外搜索乙酰化或 腺苷酸化。将开发一种体外运动测定方法， 将允许快速比较切换的影响 提纯的细胞质成分。判断运动能力的几种方法 细胞群体的趋化性将得到改善。最后， 将对系留微蜂窝的旋转行为进行分析 确定电机在以下位置运行时的相关切换统计数据 速度很快。这将有助于我们更好地理解 同一细胞上不同鞭毛的同步，并允许 更准确地预测游泳行为，基于 系留细胞分析结果。长远的目标是 感觉转导在分子水平上的描述 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.