Pheromone-induced polarization is dependent on the Fus3p MAPK acting through the formin Bni1p.
During mating, budding yeast cells reorient growth toward the highest concentration of pheromone. Bni1p, a formin homologue, is required for this polarized growth by facilitating cortical actin cable assembly. Fus3p, a pheromone-activated MAP kinase, is required for pheromone signaling and cell fusion. We show that Fus3p phosphorylates Bni1p in vitro, and phosphorylation of Bni1p in vivo during the pheromone response is dependent on Fus3p. fus3 mutants exhibited multiple phenotypes similar to bni1 mutants, including defects in actin and cell polarization, as well as Kar9p and cytoplasmic microtubule localization. Disruption of the interaction between Fus3p and the receptor-associated Galpha subunit caused similar mutant phenotypes. After pheromone treatment, Bni1p-GFP and Spa2p failed to localize to the cortex of fus3 mutants, and cell wall growth became completely unpolarized. Bni1p overexpression suppressed the actin assembly, cell polarization, and cell fusion defects. These data suggest a model wherein activated Fus3p is recruited back to the cortex, where it activates Bni1p to promote polarization and cell fusion.
Matheos
Dina
D
Department of Molecular Biology, Princeton University, Princeton, NJ 08544-1014, USA.
Metodiev
Metodi
M
Muller
Eric
E
Stone
David
D
Rose
Mark D
MD
D008841:Actin Cytoskeleton / Q000378:metabolism; D002465:Cell Movement / Q000235:genetics / Q000502:physiology*; D016764:Cell Polarity / Q000235:genetics / Q000502:physiology*; D048429:Cell Size / Q000235:genetics; D003598:Cytoskeletal Proteins; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000235:genetics; D008840:Microfilament Proteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010675:Pheromones / Q000378:metabolism*; D010766:Phosphorylation; D012098:Reproduction / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
C105191:Bni1 protein, S cerevisiae; D003598:Cytoskeletal Proteins; C110443:KAR9 protein, S cerevisiae; D008840:Microfilament Proteins; D009687:Nuclear Proteins; D010675:Pheromones; C065889:SPA2 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C075580:FUS3 protein, S cerevisiae; D020928:Mitogen-Activated Protein Kinases; D019204:GTP-Binding Proteins