Sorting out secretion

Proteins that are destined to be secreted from a cell undergo a multistep sorting and transport process, but until recently a critical portion of the secretory pathway—the transport of cargo from the Golgi apparatus—has been difficult to dissect. On page 271, Harsay and Schekman show that one population of yeast secretory proteins apparently takes a detour through an endosomal compartment on its way from the Golgi apparatus to the cell surface. Although some types of mammalian cells appear to use a secretory pathway involving endosomes, the new work is the first demonstration of such a system in yeast, a model system that should help define additional steps in this poorly understood process.

Previous work demonstrated that yeast sec6 mutants exhibit a post-Golgi secretion defect that causes the accumulation of two populations of secretory vesicles, distinguished...