Schematic depiction of septin recruitment and septin-collar formation during
the cell cycle of budding yeast. Recruitment of either a patch or cap of
septins to the incipient bud site and its rapid conversion into a rimmed
disk require the small GTPase, Cdc42. Stabilization of the disk and its
transformation into a filamentous collar requires phosphorylation by two
proteins kinases, Cla4 and Gin4 (and, perhaps, others), plus binding of GTP
to Cdc10 and Cdc12 in the septin complex. At cytokinesis, the collar splits
into two separate rings, which are disassembled after cell separation.
Confocal fluorescence images (GFP–Cdc12) were kindly provided by
Jeroen Dobbelaere (ETH, Zürich, Switzerland).