title: A role for Yip1p in COPII vesicle biogenesis.
abstract: Yeast Ypt1p-interacting protein (Yip1p) belongs to a conserved family of transmembrane proteins that interact with Rab GTPases. We encountered Yip1p as a constituent of ER-derived transport vesicles, leading us to hypothesize a direct role for this protein in transport through the early secretory pathway. Using a cell-free assay that recapitulates protein transport from the ER to the Golgi complex, we find that affinity-purified antibodies directed against the hydrophilic amino terminus of Yip1p potently inhibit transport. Surprisingly, inhibition is specific to the COPII-dependent budding stage. In support of this in vitro observation, strains bearing the temperature-sensitive yip1-4 allele accumulate ER membranes at a nonpermissive temperature, with no apparent accumulation of vesicle intermediates. Genetic interaction analyses of the yip1-4 mutation corroborate a function in ER budding. Finally, ordering experiments show that preincubation of ER membranes with COPII proteins decreases sensitivity to anti-Yip1p antibodies, indicating an early requirement for Yip1p in vesicle formation. We propose that Yip1p has a previously unappreciated role in COPII vesicle biogenesis.
authors.affiliation: Department of Biochemistry, Dartmouth Medical School, Hanover, NH 03755, USA.
authors.forename: Matthew
authors.initials: M
authors.lastname: Heidtman
authors.forename: Catherine Z
authors.initials: CZ
authors.lastname: Chen
authors.forename: Ruth N
authors.initials: RN
authors.lastname: Collins
authors.forename: Charles
authors.initials: C
authors.lastname: Barlowe
mesh_terms: D022181:COP-Coated Vesicles / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D008565:Membrane Proteins; D008854:Microscopy, Electron; D012441:Saccharomyces cerevisiae / Q000378:metabolism / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins
chemical_list: D005656:Fungal Proteins; D008565:Membrane Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C414462:Yip1 protein, S cerevisiae