title: The Sec1/Munc18 protein, Vps33p, functions at the endosome and the vacuole of Saccharomyces cerevisiae.
abstract: The Sec1/Munc18 (SM) family of proteins is thought to impart compartmental specificity to vesicle fusion reactions. Here we report characterization of Vps33p, an SM family member previously thought to act exclusively at the vacuolar membrane with the vacuolar syntaxin Vam3p. Vacuolar morphology of vps33Delta cells resembles that of cells lacking both Vam3p and the endosomal syntaxin Pep12p, suggesting that Vps33p may function with these syntaxins at the vacuole and the endosome. Consistent with this, vps33 mutants secrete the Golgi precursor form of the vacuolar hydrolase CPY into the medium. We also demonstrate that Vps33p acts at other steps, for vps33 mutants show severe defects in endocytosis at the late endosome. At the endosome, Vps33p and other class C members exist as a complex with Vps8p, a protein previously known to act in transport between the late Golgi and the endosome. Vps33p also interacts with Pep12p, a known interactor of the SM protein Vps45p. High copy PEP7/VAC1 suppresses vacuolar morphology defects of vps33 mutants. These findings demonstrate that Vps33p functions at multiple trafficking steps and is not limited to action at the vacuolar membrane. This is the first report demonstrating the involvement of a single syntaxin with two SM proteins at the same organelle.
authors.affiliation: Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA. shoba@andrew.cmu.edu
authors.forename: Shoba
authors.initials: S
authors.lastname: Subramanian
authors.forename: Carol A
authors.initials: CA
authors.lastname: Woolford
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Jones
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D043402:Cathepsin A / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D017353:Gene Deletion; D006031:Glycosylation; D006056:Golgi Apparatus / Q000378:metabolism; D000072235:Mating Factor; D008565:Membrane Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins / Q000737:chemistry*; D010455:Peptides / Q000378:metabolism; D011485:Protein Binding; D011498:Protein Precursors / Q000378:metabolism; D050765:Qa-SNARE Proteins; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014617:Vacuoles / Q000378:metabolism* / Q000648:ultrastructure; D033921:Vesicular Transport Proteins / Q000737:chemistry* / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D003598:Cytoskeletal Proteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; C081224:PEP12 protein, S cerevisiae; C106978:PEP7 protein, S cerevisiae; D010455:Peptides; D011498:Protein Precursors; D050765:Qa-SNARE Proteins; C497931:SEC1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C107706:VAM3 protein, S cerevisiae; C065454:VPS33 protein, S cerevisiae; C103153:VPS8 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D000072235:Mating Factor; D043402:Cathepsin A