FIG. 4.

Binding of wild-type and mutant CheY to fluoresceinated CheZ. The steady-state fluorescence anisotropy of fluoresceinated CheZ (0.13 μM) was measured in the presence of increasing concentrations of activated CheY. Activation was accomplished by the addition of acetyl phosphate (12 mM), which phosphorylates CheY, or BeF₃⁻ (0.1 mM BeCl₂, 10 mM NaF). Measurements are shown for wild-type CheY (squares), CheYE89A (diamonds), and CheYE89Q (triangles). Open symbols show activation by phosphorylation, and solid symbols show activation by BeF₃⁻.