Figure 7.

Model of intracellular signaling. The receptor patch, including chemoreceptor, histidine kinase CheA, phosphatase CheZ, and CheW is localized at the left side of E. coli cell. Motor 1 is the closest to the chemoreceptor patch, and motor 2 is the farthest from it (top). A transient increase and decrease in the concentration of a signal protein (CheY-P) from the chemoreceptor patch, which is probably a wavelike change in under a second, triggers and regulates the coordinated switching of flagellar motors. The intracellular signaling molecules were generated at the chemoreceptor patch and propagated toward to another cell pole. The concentration of CheY-P above the threshold for switching increases around motor 1 first, and the increasing then follows around motor 2. In addition, the decreasing of concentration of CheY-P around motor 1 precedes that of around motor 2 (middle). In this case, motor 1 closest to the chemoreceptor patch precedes motor 2 farthest from it in switching CCW-to-CW and CW-to-CCW (bottom). The phosphatase activity of CheZ as well as the diffusion of CheY-P molecules would be important to produce a wavelike change in the CheY-P concentration.