Rescue of a CP projection mutant pf6 in rsp tag mutant backgrounds. (A) Motility of pf6 rsp mutants. pf6 rsp3C, 4C, and 6C mutants showed recovery of motility. (B) Motility of pf6 rsp4C mutants having different tags. There is a positive correlation between recovery of motility and the size of the tags on RSP4. (A and B) Diagrams below the charts indicate the positions of tags (red stars) on the RS. Because rescued strains made frequent turns after short straight swimming, swimming speed was measured by taking the mean speed between one turn and the next. (B) The crystal structures of 3×HA (violet, predicted structure), BCCP (green, Protein Data Bank accession no. 1BOD), and GFP (blue, Protein Data Bank accession no. 1EMA) are shown for size comparison. The tertiary structure of 3×HA was predicted using the PROTINFO tool (Hung and Samudrala, 2003). (C) Comparison of the CP–RS gap and the size of tags fused to RSP4. The crystal structures of 3×HA (violet), BCCP (green), GFP (blue), and streptavidin (red; Protein Data Bank accession no. 4JO6) were superimposed above the RS head. Images of averaged subtomogram were colored based on the distance from the CP–RS interface. (D) Motility of pf6 oda/ida rsp4C-GFP mutants. As forward swimming was not observed in any of the mutant strains, percentages of motile cells were calculated by counting rotating or jiggling cells. The p-values were calculated using Student’s t test. (A, B, and D) Means ± SEM for mean percentages of swimming/motile cells and mean swimming speeds were calculated from 10 measurements and 20 cells, respectively.