Compartmentalization of the cell cortex by septins is required for maintenance of cell polarity in yeast

Formation and maintenance of specialized plasma membrane domains are crucia l for many biological processes, such as cell polarization and signaling. D uring isotropic bud growth, the yeast cell periphery is divided into two do mains: the bud surface, an active site of exocytosis and growth, and the re latively quiescent surface of the mother cell. We found that cells lacking septins at the bud neck failed to maintain the exocytosis and morphogenesis factors Spa2, Sec3, Sec5, and Myo2 in the bud during isotropic growth. Fur thermore, we found that septins were required for proper regulation of acti n patch stability; septin-defective cells permitted to enter isotropic grow th lost actin and growth polarity. We propose that septins maintain cell po larity by specifying a boundary between cortical domains.