The exocyst is a conserved protein complex proposed to mediate tethering of the Golgi-derived secretory vesicles at plasma membrane in yeast. SEB1/SBH1, encoding the beta subunit of the Sec6lp ER translocation complex, was previously isolated as a multicopy suppressor of the temperature-sensitive sec 15-1 mutant defective for one subunit of the exocyst complex. We now report that overexpression of SEB1 suppresses the growth defect in all exocyst sec mutants. In addition, overexpression of SEC61 or SSS1 encoding the other two subunits of the Sec61 p complex suppress the growth defects of several exocyst mutants. In wild type cells overexpression of SEB1 as well as that of SEC4, which encodes a small rab GTPase required for exocytosis, resulted in increased production of secreted proteins. Furthermore, Seblp 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 Sec15p. The interaction between Seb1p and Sec15p was abolished in sec15-1 mutant cells and was restored upon SEB1 overexpression. These findings propose a novel functional link between the ER translocon and the exocyst complex.
|Conference||21st International Conference on Yeast Genetics and Molecular Biology, Yeast 2003|
|Period||7/07/03 → 12/07/03|