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© The Rockefeller University Press,
0021-9525/1998//1473 $5.00
The Journal of Cell Biology, Volume 142, Number 6,
, 1998 1473-1485
Regular Articles |
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 MAT
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 MAT 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.
Key Words: yeast • mating • morphogenesis • cell fusion • metalloprotease • GTPase
Abbreviations used in this paper: DAPI, 4,6-diamidino-2-phenylindole; GFP, green fluorescent protein; ORF, open reading frame; Wt, wild-type.
Address all correspondence to Lorraine Marsh, Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461. Tel.: (718) 430-2841. Fax: (718) 430-8574. E-mail: marsh{at}aecom.yu.edu
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