title: The itinerary of a vesicle component, Aut7p/Cvt5p, terminates in the yeast vacuole via the autophagy/Cvt pathways.
abstract: Aminopeptidase I (API) is delivered to the yeast vacuole by one of two alternative pathways, cytoplasm to vacuole targeting (Cvt) or autophagy, depending on nutrient conditions. Genetic, morphological, and biochemical studies indicate that the two pathways share many of the same molecular components. The Cvt pathway functions during vegetative growth, while autophagy is induced during starvation. Both pathways involve the formation of cytosolic vesicles that fuse with the vacuole. In either case, the mechanism of vesicle formation is not known. Autophagic uptake displays a greater capacity for cytosolic protein sequestration. This suggests the involvement of an inducible protein(s) that allows the vesicle-forming machinery to adapt to the increased degradative needs of the cell. We have analyzed the biosynthesis of Aut7p, a protein required for both pathways. We find Aut7p expression is induced by nitrogen starvation. Aut7p is degraded by a process dependent on both proteinase A and Cvt/autophagy components. Protease accessibility assays demonstrate that Aut7p is located within vesicles in strains defective in vesicle delivery or breakdown. Finally, the aut7/cvt5 mutant accumulates precursor API at a stage prior to vesicle completion. These data suggest that Aut7p is induced during autophagy and delivered to the vacuole together with precursor API by Cvt/autophagic vesicles.
authors.affiliation: Section of Microbiology, University of California, Davis, California 95616, USA.
authors.forename: W P
authors.initials: WP
authors.lastname: Huang
authors.forename: S V
authors.initials: SV
authors.lastname: Scott
authors.forename: J
authors.initials: J
authors.lastname: Kim
authors.forename: D J
authors.initials: DJ
authors.lastname: Klionsky
mesh_terms: D000071190:Autophagy-Related Protein 8 Family; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000737:chemistry; D003001:Cloning, Molecular; D010450:Endopeptidases / Q000378:metabolism; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology; D007700:Kinetics; D008565:Membrane Proteins / Q000737:chemistry; D008869:Microtubule-Associated Proteins / Q000737:chemistry* / Q000235:genetics / Q000502:physiology; D009154:Mutation; D009584:Nitrogen / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology; D012441:Saccharomyces cerevisiae / Q000737:chemistry; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions; D013997:Time Factors; D014617:Vacuoles / Q000737:chemistry*
chemical_list: C113757:ATG8 protein, S cerevisiae; D000071190:Autophagy-Related Protein 8 Family; D005656:Fungal Proteins; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D029701:Saccharomyces cerevisiae Proteins; D010450:Endopeptidases; D009584:Nitrogen