The Golgi-resident protease Kex2 acts in conjunction with Prm1 to facilitate cell fusion during yeast mating.
The molecular machines that mediate cell fusion are unknown. Previously, we identified a multispanning transmembrane protein, Prm1 (pheromone-regulated membrane protein 1), that acts during yeast mating (Heiman, M.G., and P. Walter. 2000. J. Cell Biol. 151:719-730). Without Prm1, a substantial fraction of mating pairs arrest with their plasma membranes tightly apposed yet unfused. In this study, we show that lack of the Golgi-resident protease Kex2 strongly enhances the cell fusion defect of Prm1-deficient mating pairs and causes a mild fusion defect in otherwise wild-type mating pairs. Lack of the Kex1 protease but not the Ste13 protease results in similar defects. Deltakex2 and Deltakex1 fusion defects were suppressed by osmotic support, a trait shared with mutants defective in cell wall remodeling. In contrast, other cell wall mutants do not enhance the Deltaprm1 fusion defect. Electron microscopy of Deltakex2-derived mating pairs revealed novel extracellular blebs at presumptive sites of fusion. Kex2 and Kex1 may promote cell fusion by proteolytically processing substrates that act in parallel to Prm1 as an alternative fusion machine, as cell wall components, or both.
Heiman
Maxwell G
MG
Howard Hughes Medical Institute, Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
Engel
Alex
A
Walter
Peter
P
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000502:physiology; D002268:Carboxypeptidases / Q000235:genetics / Q000502:physiology; D027682:Cation Transport Proteins / Q000235:genetics / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002473:Cell Wall / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D003224:Congo Red / Q000494:pharmacology; D022162:Cytoplasmic Vesicles / Q000378:metabolism / Q000648:ultrastructure; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases / Q000235:genetics / Q000502:physiology; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology; D043326:Glucan 1,3-beta-Glucosidase / Q000235:genetics / Q000502:physiology; D006023:Glycoproteins / Q000235:genetics / Q000502:physiology; D006056:Golgi Apparatus / Q000201:enzymology*; D006360:Heat-Shock Proteins / Q000235:genetics / Q000502:physiology; D008561:Membrane Fusion / Q000502:physiology; D008565:Membrane Proteins / Q000235:genetics / Q000502:physiology*; D008854:Microscopy, Electron; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000502:physiology; D008954:Models, Biological; D009154:Mutation; D009997:Osmotic Pressure; D043484:Proprotein Convertases / Q000235:genetics / Q000502:physiology*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics / Q000502:physiology*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D000254:Sodium-Potassium-Exchanging ATPase
D027682:Cation Transport Proteins; D003598:Cytoskeletal Proteins; C086375:ENA1 protein, S cerevisiae; C490024:FUS1 protein, S cerevisiae; C095898:FUS2 protein, S cerevisiae; D005656:Fungal Proteins; D006023:Glycoproteins; C074229:HSP150 protein, S cerevisiae; D006360:Heat-Shock Proteins; D008565:Membrane Proteins; C423367:PIR1 protein, S cerevisiae; C499613:PRM1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D003224:Congo Red; D020928:Mitogen-Activated Protein Kinases; C072724:SLT2 protein, S cerevisiae; C468487:EXG1 protein, S cerevisiae; D043326:Glucan 1,3-beta-Glucosidase; D002268:Carboxypeptidases; D004152:Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; C061833:STE13 protein, S cerevisiae; C078874:carboxypeptidase D; D043484:Proprotein Convertases; C058751:KEX2 protein, S cerevisiae; D000251:Adenosine Triphosphatases; D000254:Sodium-Potassium-Exchanging ATPase