Projects -Fluorescent flagella -Swimming without flagella -Gliding motility -Twitching motility -Fluorescent chemotaxis proteins -Chemotactic signaling studied by FRET -Models of the chemotactic system -Motor force generation -Switching under load

Models of the chemotactic system In collaboration with Yuhai Tu (IBM) we have developed a model for chemotactic signaling in Escherichia coli that explains in a unified way responses to time-varying stimuli: exponential ramps of nonmetabolizable attractants, exponentiated sine waves, impulses, successive steps, etc. When such experiments were done in the 1970's and 80's, we naively assumed that responses (measured with tethered cells) were proportional to the time rate of change of receptor occupany. We know now about allosteric amplification in receptor clusters, effects of receptor methylation and demethylation on the activity of the receptor kinase CheA, phosphorylation of the signaling protein CheY by CheA, dephosphorylation of CheY-P by the phosphatase CheZ, etc. We think that we now understand how changes in the activity of the receptor kinase (and hence the concentration of the signaling molecule CheY-P) depend upon changes in concentrations of attractants and repellents. References Tu, Y., Shimizu, T.S. and Berg, H.C. Modeling the chemotactic response of Escherichia coli to time-varying stimuli. Proc. Natl. Acad. Sci. USA, in press.

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