A role for a protease in morphogenic responses during yeast cell fusion.
Cell fusion during yeast mating provides a model for signaling-controlled changes at the cell surface. We identified the AXL1 gene in a screen for genes required for cell fusion in both mating types during mating. AXL1 is a pheromone-inducible gene required for axial bud site selection in haploid yeast and for proteolytic maturation of a-factor. Two other bud site selection genes, RSR1, encoding a small GTPase, and BUD3, were also required for efficient cell fusion. Based on double mutant analysis, AXL1 in a MATalpha strain acted genetically in the same pathway with FUS2, a fusion-dedicated gene. Electron microscopy of axl1, rsr1, and fus2 prezygotes revealed similar defects in nuclear migration, vesicle accumulation, cell wall degradation, and membrane fusion during cell fusion. The axl1 and rsr1 mutants exhibited defects in pheromone-induced morphogenesis. AXL1 protease function was required in MATalpha strains for fusion during mating. The ability of the Rsr1p GTPase to cycle was required for efficient cell fusion, as it is for bud site selection. During conjugation, vegetative functions may be redeployed under the control of pheromone signaling for mating purposes. Since Rsr1p has been reported to physically associate with Cdc24p and Bem1p components of the pheromone response pathway, we suggest that the bud site selection genes Rsr1p and Axl1p may act to mediate pheromone control of Fus2p-based fusion events during mating.
Elia
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Department of Cell Biology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Marsh
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D018797:Cell Cycle Proteins / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000235:genetics; D010450:Endopeptidases / Q000235:genetics / Q000502:physiology*; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D020963:GTP Phosphohydrolase-Linked Elongation Factors / Q000235:genetics / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000378:metabolism; D005816:Genetic Complementation Test; D008565:Membrane Proteins / Q000235:genetics; D008666:Metalloendopeptidases; D009024:Morphogenesis; D010445:Peptide Elongation Factors / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins; D013347:Subcellular Fractions; D015053:Zygote; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020691:rab GTP-Binding Proteins
C093319:BUD3 protein, S cerevisiae; D018797:Cell Cycle Proteins; D003598:Cytoskeletal Proteins; C095898:FUS2 protein, S cerevisiae; D005656:Fungal Proteins; D008565:Membrane Proteins; D010445:Peptide Elongation Factors; D029701:Saccharomyces cerevisiae Proteins; C111584:YEF3 protein, S cerevisiae; D010450:Endopeptidases; C090850:AXL1 protein, S cerevisiae; D008666:Metalloendopeptidases; D020963:GTP Phosphohydrolase-Linked Elongation Factors; D019204:GTP-Binding Proteins; C084013:RSR1 protein, S cerevisiae; D020846:cdc42 GTP-Binding Protein, Saccharomyces cerevisiae; D020691:rab GTP-Binding Proteins