The mechanism by which soluble proteins, such as carboxypeptidase Y, reach the vacuole in Saccharomyces cerevisiae is very similar to the mechanism of lysosomal protein sorting in mammalian cells. Vps10p is a receptor for transport of soluble vacuolar proteins in S. cerevisiae. vps10+, a gene encoding a homologue of S. cerevisiae PEP1 /VPS10, has been identified and deleted from the fission yeast Schizosaccharomyces pombe. Deletion of the vps10+ gene resulted in missorting and secretion of Sch. pombe vacuolar carboxypeptidase Cpy1p, indicating that it is required for targeting Cpy1p to the vacuole. Sch. pombe Vps10p (SpVps10p) is a type I transmembrane protein and its C-terminal cytoplasmic tail domain is essential for Cpy1p transport to the vacuole. Cells expressing green fluorescent protein-tagged SpVps10p produced a punctate pattern of fluorescence, indicating that SpVpsl0p was largely localized in the Golgi compartment. In addition, Sch. pombe vps26+, vps29+ and vps35+, encoding homologues of the S. cerevisiae retromer components VPS26, VPS29 and VPS35, were identified and deleted. Fluorescence microscopy demonstrated that SpVps10p mislocalized to the vacuolar membrane in these mutants. These results indicate that the vps26+, vps29+ and vps35+ gene products are required for retrograde transport of SpVps10p from the prevacuolar compartment backto the Golgi in Sch. pombe cells.
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