Many types of cells maintain specialized plasma membrane domains to which different subsets of secretory vesicles are targeted, enabling the cells' performance of specific functions. The budding yeast Saccharomyces cerevisiae spatially and temporally regulates exocytosis, directing surface growth and secretion to different plasma membrane sites at different cell cycle stages (21). In very small buds, secretion occurs over the entire bud surface, but as the bud enlarges growth is directed to the bud tip. When the bud is two-thirds the size of the mother cell, secretion becomes isotropic over the entire bud surface. Late in the cell cycle, new material is inserted at the neck between mother and daughter cells, resulting in cytokinesis and septation.
The accurate delivery of vesicles to sites of exocytosis requires both actin-dependent vesicle transport and actin-independent establishment of a vesicle-receiving station. The first step, polarized vesicle transport, also involves a rab...
