Figure 3

Calibration of the model. (A and B) Fourier transformed linear response function. (A) Magnitude of the response function of the rotary motor measured by Block et al. [26] (circles) and Segall et al. [27] (plus symbols). The fit of our model is shown by the solid line. The dashed line represents a 3rd-order filter for comparison. (B) Magnitude (left) and phase (right) of the response function at the level of the response regulator CheY measured by Shimizu et al. [28]. The symbols are measurements at 22°C (circles) and 32°C (plus symbols). Grey lines represent the fit of our model to the magnitude of the response. (C) Switching rates of the motor from CCW to CW rotation k₊ (squares) and from CW to CCW rotation k_- (circles) as a function of the concentration of signalling-active unphosphorylated double-mutant Y**. The cellular concentration of Y** varied as a result of induced expression in cells in which wild-type CheY and other cytoplasmic chemotaxis proteins had been deleted. A fit using the model of Turner et al. [39] is shown as well (solid and dashed lines; cf. Methods).