Protein-protein interactions governing septin heteropentamer assembly and septin filament organization in Saccharomyces cerevisiae.

Mitotic yeast (Saccharomyces cerevisiae) cells express five related septins (Cdc3, Cdc10, Cdc11, Cdc12, and Shs1) that form a cortical filamentous collar at the mother-bud neck necessary for normal morphogenesis and cytokinesis. All five possess an N-terminal GTPase domain and, except for Cdc10, a C-terminal extension (CTE) containing a predicted coiled coil. Here, we show that the CTEs of Cdc3 and Cdc12 are essential for their association and for the function of both septins in vivo.

Coupling morphogenesis to mitotic entry.

In eukaryotes, cyclin B-bound cyclin-dependent protein kinase 1 promotes mitotic entry but is held in check, in part, by Wee1 protein kinase. Timely mitotic entry in budding yeast requires inactivation of Swe1 (Wee1 ortholog). Perturbations of the septin collar at the bud neck lead to Swe1 stabilization, delaying the G(2)/M transition.

Targeting of Nir2 to lipid droplets is regulated by a specific threonine residue within its PI-transfer domain.

Nir2, like its Drosophila homolog retinal degeneration B (RdgB), contains an N-terminal phosphatidylinositol-transfer protein (PI-TP)-like domain. Previous studies have suggested that RdgB plays an important role in the fly phototransduction cascade and that its PI-transfer domain is critical for this function. In this domain, a specific mutation, T59E, induces a dominant retinal degeneration phenotype.