FIGURE 7.

Mutational data mapped onto the model of the FliN₄-FliM_C-FliN₄ unit. A, FliM_C-FliN binding data mapped onto a stereoview of the FliN₄-FliM_C-FliN₄ model. Positions where mutations disrupted binding are colored red, and positions where binding was unaffected are blue. B, positions of Cys replacements that had the largest effect on function. Mutations at the four positions indicated in FliM_C and position 126 in FliN reduced swarming to about half of that of the wild type; the mutation at position 134 in FliN reduced function to ∼10% of that of the wild type. (Functional data on all Cys mutants are provided in the supplemental data.) C, additional mutations. Four mutations in FliN that gave a moderate assembly defect and severe motility defect, isolated in an extensive study of spontaneous mutants (13), are shown in orange. These cluster on a surface of FliN that is in contact with FliM_C (the left-hand interface in the figure). Two additional mutations that were made as tests of the model are indicated in red-orange (FliM position 292) and purple (FliN position 87). D, effects of the site-directed mutations I292E and V87D. Both mutations prevented swarming in the soft agar assay (upper panels) and FliM-FliN binding in the pulldown assay (lower panels). cont, control; wt, wild-type.