Mso1p: A yeast protein that functions in secretion and interacts physically and genetically with Sec1p

Mso1p: A yeast protein that functions in secretion and interacts physically and genetically with Sec1p

^*Department of Medical Immunology and Microbiology, Uppsala University, Uppsala Biomedical Center, Box 582, S-751 23 Uppsala, Sweden; ^¶VTT Biotechnology and Food Research, P.O. Box 1500, FIN-02044 VTT, Finland; and ^†Ludwig Institute for Cancer Research, Uppsala Branch, Uppsala Biomedical Center, Box 595, S-751 24 Uppsala, Sweden

Abstract

The yeast Sec1p protein functions in the docking of secretory transport vesicles to the plasma membrane. We previously have cloned two yeast genes encoding syntaxins, SSO1 and SSO2, as suppressors of the temperature-sensitive sec1–1 mutation. We now describe a third suppressor of sec1–1, which we call MSO1. Unlike SSO1 and SSO2, MSO1 is specific for sec1 and does not suppress mutations in any other SEC genes. MSO1 encodes a small hydrophilic protein that is enriched in a microsomal membrane fraction. Cells that lack MSO1 are viable, but they accumulate secretory vesicles in the bud, indicating that the terminal step in secretion is partially impaired. Moreover, loss of MSO1 shows synthetic lethality with mutations in SEC1, SEC2, and SEC4, and other synthetic phenotypes with mutations in several other late-acting SEC genes. We further found that Mso1p interacts with Sec1p both in vitro and in the two-hybrid system. These findings suggest that Mso1p is a component of the secretory vesicle docking complex whose function is closely associated with that of Sec1p.

Footnotes

↵ ‡ Present address: Institute of Microbiology, Johann Wolfgang Goethe University, Marie Curie Strasse 9, D-60439 Frankfurt, Germany.
↵ § M.K.A. and J.J. contributed equally to this work.
↵ ‖ To whom reprint requests should be addressed. e-mail: Ronne{at}bmc.uu.se.
Randy Schekman, University of California, Berkeley, CA
Data deposition: The sequence reported in this paper has been deposited with the GenBank database (accession no. U56416).
ABBREVIATION:

NTA,

nitrilotriacetic acid