Septin deficiencies in budding yeast cause cytokinesis defects and the loss of filaments at the mother–bud neck. And mammalian septins are found at cleavage furrows. But three papers in this issue suggest that the septins may be more important as a docking site for proteins than as a cytoskeletal mediator of cytokinesis.
Frazier et al. (page ) use antibodies to yeast Cdc3p to isolate a complex of four septins: Cdc3p, Cdc10p, Cdc11p, and Cdc12p. The yeast septins extend to form filaments of over 1,500 nm in length when dialyzed into physiological salt.
Yeast neck filaments were originally thought to be oriented around the bud neck. But the repeat length for the polymer in vitro is 32 nm—the same size as the gap between neck filaments. Thus the electron microscopy may be detecting a repeating structure in cells (perhaps a cross-linker) and not the filaments themselves. This led senior author...
