A novel septin-associated protein, Syp1p, is required for normal cell cycle-dependent septin cytoskeleton dynamics in yeast.

Septins are a family of GTP-binding proteins whose heterooligomeric complex is the basic structural element of the septin filaments found in many eukaryotic organisms. In budding yeast, septins are mainly confined at the mother-daughter junction and are required for cell morphogenesis and division. Septins undergo assembly and disassembly in accordance with the progression of the cell cycle. In this report, we identified the yeast protein Syp1p as a new regulator of septin dynamics. Syp1p colocalizes with septins throughout most of the cell cycle. Syp1p interacts with the septin subunit Cdc10p and can be precipitated by Cdc10p and Cdc12p. In the syp1Delta mutant, both formation of a complete septin ring at the incipient bud site and disassembly of the septin ring in later stages of cell division are significantly delayed. In addition, overexpression of Syp1p causes marked acceleration of septin disassembly. The fluorescence recovery after photobleaching (FRAP) assay further showed that Syp1p promotes septin turnover in different cell cycle stages. These results suggest that Syp1p is involved in the regulation of cell cycle-dependent dynamics of the septin cytoskeleton in yeast.