The yeast endocytic membrane transport system

Progress has been made recently in visualizing the structures and organelle s responsible for endocytic membrane traffic from the cell surface to the l ysosome-like vacuole in Saccharomyces cerevisiae. This, together with the r ecent discovery of several new membrane trafficking pathways connecting the se organelles, has led to a quantum leap in our understanding of the S. cer evisiae endocytic pathway. We now know that although the cortical actin cyt oskeleton is required for the internalization step of endocytosis, the inte rnalization event occurs at furrow-like invaginations of the plasma membran e, which are distinct from cortical actin patches. Internalized material is taken into the cell in the form of small (30-50 nm diameter) vesicles and delivered to tubulo-vesicular early endosomes at the cell periphery. Subseq uently, the internalized material arrives in multivesicular late endosomes adjacent to the vacuole. Recent microscopy evidence suggests that transfer from late endosomes to the vacuole may involve direct fusion of late endoso mes with the vacuole. The visualization of the S. cerevisiae endocytic path way has revealed similarities to endocytic pathways visualized in higher eu karyotes. (C) 2000 Wiley-Liss, Inc.