title: The role of Sec3p in secretory vesicle targeting and exocyst complex assembly.
abstract: During membrane trafficking, vesicular carriers are transported and tethered to their cognate acceptor compartments before soluble N-ethylmaleimide-sensitive factor attachment protein (SNARE)-mediated membrane fusion. The exocyst complex was believed to target and tether post-Golgi secretory vesicles to the plasma membrane during exocytosis. However, no definitive experimental evidence is available to support this notion. We developed an ectopic targeting assay in yeast in which each of the eight exocyst subunits was expressed on the surface of mitochondria. We find that most of the exocyst subunits were able to recruit the other members of the complex there, and mistargeting of the exocyst led to secretion defects in cells. On the other hand, only the ectopically located Sec3p subunit is capable of recruiting secretory vesicles to mitochondria. Our assay also suggests that both cytosolic diffusion and cytoskeleton-based transport mediate the recruitment of exocyst subunits and secretory vesicles during exocytosis. In addition, the Rab GTPase Sec4p and its guanine nucleotide exchange factor Sec2p regulate the assembly of the exocyst complex. Our study helps to establish the role of the exocyst subunits in tethering and allows the investigation of the mechanisms that regulate vesicle tethering during exocytosis.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018.
authors.forename: Guangzuo
authors.initials: G
authors.lastname: Luo
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, PA 19104-6018 guowei@sas.upenn.edu.
authors.forename: Wei
authors.initials: W
authors.lastname: Guo
mesh_terms: D001692:Biological Transport / Q000235:genetics*; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D003593:Cytoplasm / Q000235:genetics; D005089:Exocytosis / Q000235:genetics*; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D022142:Secretory Vesicles / Q000235:genetics / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C064456:SEC2 protein, S cerevisiae; C103130:SEC3 protein, S cerevisiae; D050600:SNARE Proteins; D029701:Saccharomyces cerevisiae Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins