title: Bem1p contributes to secretory pathway polarization through a direct interaction with Exo70p.
abstract: The exocyst serves to tether secretory vesicles to cortical sites specified by polarity determinants, in preparation for fusion with the plasma membrane. Although most exocyst components are brought to these sites by riding on secretory vesicles as they are actively transported along actin cables, Exo70p displays actin-independent localization to these sites, implying an interaction with a polarity determinant. Here we show that Exo70p directly and specifically binds to the polarity determinant scaffold protein Bem1p. The interaction involves multiple domains of both Exo70p and Bem1p. Mutations in Exo70p that disrupt its interaction with Bem1, without impairing its interactions with other known binding partners, lead to the loss of actin-independent localization. Synthetic genetic interactions confirm the importance of the Exo70p-Bem1p interaction, although there is some possible redundancy with Sec3p and Sec15p, other exocyst components that also interact with polarity determinants. Similar to Sec3p, the actin-independent localization of Exo70p requires a synergistic interaction with the phosphoinositide PI(4,5)P2.
authors.affiliation: Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92130.
authors.forename: Dongmei
authors.initials: D
authors.lastname: Liu
authors.affiliation: Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92130 pnovick@ucsd.edu.
authors.forename: Peter
authors.initials: P
authors.lastname: Novick
mesh_terms: D008841:Actin Cytoskeleton / Q000235:genetics; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites / Q000235:genetics; D018797:Cell Cycle Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000235:genetics; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D019269:Phosphatidylinositol 4,5-Diphosphate; D011485:Protein Binding / Q000235:genetics; D020033:Protein Isoforms / Q000235:genetics; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D022142:Secretory Vesicles / Q000378:metabolism*; D033921:Vesicular Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D020741:rho GTP-Binding Proteins / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; C073594:CDC24 protein, S cerevisiae; D018797:Cell Cycle Proteins; C103132:EXO70 protein, S cerevisiae; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D019269:Phosphatidylinositol 4,5-Diphosphate; D020033:Protein Isoforms; C060862:SEC15 protein, S cerevisiae; C103130:SEC3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; C073129:BEM1 protein, S cerevisiae; C107283:GIN4 protein, S cerevisiae; D018844:Cyclin-Dependent Kinases; C512892:CDC10 protein, S cerevisiae; D020558:GTP Phosphohydrolases; C074647:RHO3 protein, S cerevisiae; D020741:rho GTP-Binding Proteins