Characterization of the energy-dependent, mating factor-activated Ca 2+ influx in Saccharomyces cerevisiae

Abstract

The yeast mating pheromones, a and α factors, bind to specific G protein-coupled receptors in haploid cells and bring about both growth arrest in the early G 1 phase of the cell cycle and differentiation into mating capable cells. This induces an increase in Ca 2+ influx leading to elevated intracellular calcium concentrations, which has been shown to be essential for subsequent downstream events and the mating process itself [1]. We have characterized the α factor induced increase in cellular Ca 2+ in wild type S. cerevisiae and in the temperature-sensitive cell division cycle mutants cdc7 and cdc28 which are growth-arrested at the G 0–G 1 border at the nonpermissive temperature. We observed a 2–4 fold increase in the initial velocity of Ca 2+ influx in α factor-treated wild-type cells and in cdc7 and cdc28 cells grown at the nonpermissive temperature. Calcium influx was energy dependent, inhibited by membrane depolarization and slightly increased by hyperpolarization. Furthermore, Ca 2+ influx was sensitive to both divalent and trivalent cations, but was unaffected by nifedipine and verapamil. These data demonstrate that budding yeast possesses a regulated Ca 2+ transport mechanism, the activation of which is dependent upon exit out of the cell cycle and growth cessation. This transport mechanism has many similarities to that observed in mitogen-stimulated mammalian cells.