Autophagy and the Cytoplasm to Vacuole Targeting Pathway

One of the hallmarks of eukaryotic cells is the presence of a variety of organelles that allow the separation of various reactions into discrete subcellular compartments. It is critical that the proper proteins be efficiently sorted to each of these organelles so that they can carry out their correct function. The importance of protein targeting is underscored by the fact that many genetic diseases are associated with the absence of particular proteins from specific organelles. The yeast vacuole (figure 1) plays a central role in cellular physiology.

This organelle is analogous to the mammalian lysosome. The advantage of carrying out these studies in yeast is that this system is more amenable to various genetic and molecular genetic approaches than are higher eukaryotes. The pathways used in protein targeting, however, are quite similar so that the information we learn from studying yeast will be applicable to animal cells. The vacuole is integrally involved in numerous cellular processes. It plays a role in osmoregulation, cytosolic ion and pH homeostasis, storage of metabolites, removal of toxic substances and macromolecular degradation and recycling.