Streptavidin-dependent inhibition of motility in BCCP-RSP mutant cells. (A) Dark-field image sequences of demembranated, ATP-reactivated rsp4C cells. The interval between each frame is 1/300 s. The rsp4C cells showed normal motility in the presence of BSA, whereas in the presence of streptavidin, the cells exhibit paralyzed flagella in a slightly bent form. Bar, 10 µm. (B) Percentages of ATP-reactivated swimming cells after demembranation and addition of BSA or streptavidin. rsp3C, 4C, and 6C cells showed flagellar paralysis in response to addition of streptavidin. A smaller version of Fig. 2 B is included for reference. (C) Averaged swimming speed of ATP-reactivated swimming cells. (D) The dose-dependent percentage and speed of swimming cells relative to the concentration of streptavidin were measured. (B–D) The means ± SEM of the percentages of swimming cells and swimming speed were calculated from 10 measurements and 20 cells, respectively. (E) Mean swimming speeds of ATP-reactivated cells were measured for oda1 rsp4C, ida3 rsp4C, and ida5 rsp4C mutants. In the presence of streptavidin, oda1 rsp4C cells showed swimming with reduced speeds compared with the BSA condition, whereas ida3 rsp4C and ida5 rsp4C cells exhibited flagellar paralysis after the addition of streptavidin. The means ± SEM were calculated from 20 cells. WT, wild type.