Single-cell E. coli response to an instantaneously applied chemotactic signal.

To measure the signaling process occurring inside a single E. coli cell, a serine stimulus by instantaneous photorelease from a caged compound was applied and the results showed that the response time depended on the distance between the receptor and motor, indicating that the decreased CheY-P concentration induced by serine propagates through the cytoplasm from the receptor-kinase cluster toward the motor with a timing that is explained by the diffusion of CheY and Che-P molecules.