title: The beta subunit of the Sec61p endoplasmic reticulum translocon interacts with the exocyst complex in Saccharomyces cerevisiae.
abstract: The exocyst is a conserved protein complex proposed to mediate vesicle tethering at the plasma membrane. Previously, we identified SEB1/SBH1, encoding the beta subunit of the Sec61p ER translocation complex, as a multicopy suppressor of the sec15-1 mutant, defective for one subunit of the exocyst complex. Here we show the functional and physical interaction between components of endoplasmic reticulum translocon and the exocytosis machinery. We show that overexpression of SEB1 suppresses the growth defect in all exocyst sec mutants. In addition, overexpression of SEC61 or SSS1 encoding the other two components of the Sec61p complex suppressed the growth defects of several exocyst mutants. Seb1p was coimmunoprecipitated from yeast cell lysates with Sec15p and Sec8p, components of the exocyst complex, and with Sec4p, a secretory vesicle associated Rab GTPase that binds to Sec15p and is essential for exocytosis. The interaction between Seb1p and Sec15p was abolished in sec15-1 mutant and was restored upon SEB1 overexpression. Furthermore, in wild type cells overexpression of SEB1 as well as SEC4 resulted in increased production of secreted proteins. These findings propose a novel functional and physical link between the endoplasmic reticulum translocation complex and the exocyst.
authors.affiliation: VTT Biotechnology, P. O. Box 1500, FIN-02044 VTT, Finland.
authors.forename: Jaana H
authors.initials: JH
authors.lastname: Toikkanen
authors.forename: Karl Juha
authors.initials: KJ
authors.lastname: Miller
authors.forename: Hans
authors.initials: H
authors.lastname: Söderlund
authors.forename: Jussi
authors.initials: J
authors.lastname: Jäntti
authors.forename: Sirkka
authors.initials: S
authors.lastname: Keränen
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins; D009154:Mutation; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D000069816:SEC Translocation Channels; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D026901:Membrane Transport Proteins; D000069816:SEC Translocation Channels; C060862:SEC15 protein, S cerevisiae; C499383:SEC61 protein, S cerevisiae; C489603:SEC8 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C101188:Sbh1 protein, S cerevisiae; D033921:Vesicular Transport Proteins; D019204:GTP-Binding Proteins; C064320:SEC4 protein, S cerevisiae; D020691:rab GTP-Binding Proteins