An ER-Localized SNARE Protein Is Exported in Specific COPII Vesicles for Autophagosome Biogenesis

Abstract

The de novo formation of autophagosomes for the targeting of cytosolic material to the vacuole/lysosome is upregulated upon starvation. How autophagosomes acquire membranes remains still unclear. Here, we report that, in yeast, the endoplasmic reticulum (ER)-localized Qa/t-SNARE Ufe1 has a role in autophagy. During starvation, Ufe1 is increasingly exported from the ER and targeted to intracellular sites that contain the autophagy markers Atg8 and Atg9. In addition, Ufe1 interacts with non-ER SNARE proteins implicated in autophagosome formation. Loss of Ufe1 function impairs autophagy and results in fewer and smaller autophagosomes. Unlike conventional cargo, the ER export of Ufe1 is significantly reduced in sec23-1 cells, which affects the coat protein (COP)II complex, already at the permissive temperature. Under the same conditions, sec23-1 cells are hypersensitive to starvation and deficient in autophagy. Our data suggest that ER membranes containing Ufe1 are delivered to sites of autophagosome formation in specific COPII vesicles.