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  • The EMBO Journal (2000) 19, 4485 - 4492
  • doi:10.1093/emboj/19.17.4485

A novel Golgi membrane protein is part of a GTPase-binding protein complex involved in vesicle targeting

Hugo Matern1,2,5, Xiaoping Yang1,5, Erik Andrulis3,4, Rolf Sternglanz3, Hans-Heinrich Trepte1 and Dieter Gallwitz1

  1. Department of Molecular Genetics, Max Planck Institute for Biophysical Chemistry, 37070 Göttingen, Germany
  2. Present address: Howard Hughes Medical Institute, Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305-5428, USA
  3. Department of Biochemistry and Cell Biology, State University of New York, Stony Brook, NY 11794-5215, USA
  4. Present address: Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
  5. H.Matern and X.Yang contributed equally to this work

Correspondence to:

Dieter Gallwitz, E-mail: dgallwi1@gwdg.de

Received 27 March 2000; Accepted 19 July 2000; Revised 14 July 2000

Through two-hybrid interactions, protein affinity and localization studies, we previously identified Yip1p, an integral yeast Golgi membrane protein able to bind the Ras-like GTPases Ypt1p and Ypt31p in their GDP-bound conformation. In a further two-hybrid screen, we identified Yif1p as an interacting factor of Yip1p. We show that Yif1p is an evolutionarily conserved, essential 35.5 kDa transmembrane protein that forms a tight complex with Yip1p on Golgi membranes. The hydrophilic N-terminal half of Yif1p faces the cytosol, and according to two-hybrid analyses can interact with the transport GTPases Ypt1p, Ypt31p and Sec4p, but in contrast to Yip1p, this interaction is dispensable for Yif1 protein function. Loss of Yif1p function in conditional-lethal mutants results in a block of endoplasmic reticulum (ER)-to-Golgi protein transport and in an accumulation of ER membranes and 40–50 nm vesicles. Genetic analyses suggest that Yif1p acts downstream of Yip1p. It is inferred that Ypt GTPase binding to the Yip1p–Yif1p complex is essential for and precedes vesicle docking and fusion.

  • Keywords:

    • Golgi,
    • vesicular transport,
    • Yif1p–Yip1p complex,
    • Ypt GTPases