CONTROL OF DIRECTION OF FLAGELLAR ROTATION IN BACTERIAL CHEMOTAXIS

The motile behavior of the bacterium Escherichia coil depends on the d irection of rotation of its flagellar motors. Binding of the phosphory lated signaling molecule CheY to a motor component FliM is known to en hance clockwise rotation. It is difficult to study this interaction in vivo, because the dynamics of phosphorylation of CheY by its kinase C heA and the hydrolysis of CheY (accelerated by CheZ) are not under dir ect experimental control. Here, we examine instead the interaction wit h the flagellar motor of a double mutant CheY(13DK106YW) that is activ e without phosphorylation. The behavioral assays were carried out on t ethered cells lacking CheA and CheZ. The effects of variation in intra cellular concentration of the mutant protein were highly nonlinear. Ho wever, they can be explained by a thermal isomerization model in which the free energies of clockwise and counterclockwise states depend lin early on the amount of CheY bound.