The fla24 mutation falls in a conserved alpha-helix that leads to the strut/buttress structure. (A) Diagram of domain in the cytoplasmic dynein based on the structure of Dictyostelium cytoplasmic dynein . The stalk is extended from AAA4 and contains the microtubule-binding domain (MTBD) (in darker yellow). The strut or buttress is extended from AAA5. (B) Alignment of Dictyostelium cytoplasmic dynein and Chlamydomonas cytoplasmic dynein 1b in the AAA5 domain into the strut. A leucine (L3243) is mutated in the fla24 allele. The alpha helices above the alignment show the extent of the helices in the Dictyostelium structure. (C) Logo of the region in panel B from 52 organisms  showing conservation based on height. L3243 at position 10 in the logo is conserved in all 52 organisms. (D) Diagram (redrawn from Pazour et al. ) showing the back side of the ring that may allow information to flow between the AAA1 domain and the MTBD through the C-terminus, strut, and stalk. L3243 (indicated by a black triangle) may be critical for this communication. MTBD, microtubule-binding domain.