Fig1p facilitates Ca2+ influx and cell fusion during mating of Saccharomyces cerevisiae

Eric M. Muller, Nancy A. Mackin, Scott E. Erdman, Kyle W. Cunningham

Research output: Contribution to journalArticle

75 Scopus citations

Abstract

During the mating process of yeast cells, two Ca2+ influx pathways become activated. The resulting elevation of cytosolic free Ca 2+ activates downstream signaling factors that promote long term survival of unmated cells, but the roles of Ca2+ in conjugation have not been described. The high affinity Ca2+ influx system is composed of Cchlp and Midlp and sensitive to feedback inhibition by calcineurin, a Ca2+/calmodulin-dependent protein phosphatase. To identify components and regulators of the low affinity Ca2+ influx system (LACS), we screened a collection of pheromone-responsive genes that when deleted lead to defects in LACS activity but not high affinity Ca2+ influx system activity. Numerous factors implicated in polarized morphogenesis and cell fusion (Fus10p, Fus2p, Rvs161p, Bnilp, Spa2p, and Pea2p) were found to be necessary for LACS activity. Each of these factors was also required for activation of the cell integrity mitogen-activated protein kinase cascade during the response to α-factor. Interestingly a polytopic plasma membrane protein, Figlp, was required for LACS activity but not required for activation of Mpk1p mitogen-activated protein kinase. Mpk1p was not required for LACS activity, suggesting Mpk1p and Fig1p define two independent branches in the pheromone response pathways. Fig1p-deficient mutants exhibit defects in the cell-cell fusion step of mating, but unlike other fus1 and fus2 mutants the fusion defect of fig1 mutants can be largely suppressed by high Ca2+ conditions, which bypass the requirement for LACS. These findings suggest Figlp is an important component or regulator of LACS and provide the first evidence for a role of Ca2+ signals in the cell fusion step of mating.

Original languageEnglish (US)
Pages (from-to)38461-38469
Number of pages9
JournalJournal of Biological Chemistry
Volume278
Issue number40
DOIs
StatePublished - Oct 3 2003

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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