Fig. 5.

Receptor packing in prototype interface 2 mutants analyzed by fluorescence anisotropy. Cells of strain UU2806 [∆(cheA-cheZ) ∆(tar, tap, tsr, trg, aer)] carried two compatible plasmids: pAV45 to express the mYFP-tagged Tar [QQQQ] receptor, and derivatives of pPM25 expressing CheA/CheW in combination with an interface 2 lesion (CheA-L545S, V551A, Y558G, and CheW-X3). Cells were illuminated with polarized light at the YFP excitation wavelength, and the extent of polarization (anisotropy) in the emitted light was measured. Changes in anisotropy (∆r) elicited by α-methyl-aspartate, an attractant sensed by the Tar receptor, were normalized to the maximum ∆r value in each experiment. Baseline anisotropies and absolute anisotropy changes in these experiments are shown in Fig. S5. The gray horizontal bar indicates the times of addition and subsequent removal of 1 mM α-methyl-aspartate.