Degradation of lipid vesicles in the yeast vacuole requires function of Cvt17, a putative lipase

The vacuole/lysosome serves an essential role in allowing cellular componen ts to be degraded and recycled under starvation conditions. Vacuolar hydrol ases are key proteins in this process. In Saccharyomces cerevisiae, some re sident vacuolar hydrolases are delivered by the cytoplasm to vacuole target ing (Cvt) pathway, which shares mechanistic features with autophagy, Autoph agy is a degradative pathway that is used to degrade and recycle cellular c omponents under starvation conditions. Both the Cvt pathway and autophagy e mploy double-membrane cytosolic vesicles to deliver cargo to the vacuole, A s a result, these pathways share a common terminal step, the degradation of subvacuolar vesicles. We have identified a protein, Cvt17, which is essent ial for this membrane lytic event. Cvt17 is a membrane glycoprotein that co ntains a motif conserved in esterases and lipases. The active-site serine o f this motif is required for subvacuolar vesicle lysis, This is the first c haracterization of a putative lipase implicated in vacuolar function in yea st.