Recovery of Saccharomyces cerevisiae mating-type a cells from G1 arrest by alpha factor

Abstract

Mating-type a cells of the yeast S. cerevisiae that was specifically arrested in the G1 phase of the cell cycle by .alpha. factor, an oligopeptide pheromone made by .alpha. cells, recovered and resumed cell division after a period of inhibition which was dependent on the concentration of .alpha. factor used. These treated a cells were more resistant to .alpha. factor than untreated a cells, but lost their resistance on further cell division. Cells arrested for 6 h were no more resistant to .alpha. factor than cells arrested for only 2.5 h. Mating-type a strains could inactivate or remove .alpha. factor from the culture fluid, but 2 a sterile (nonmating) mutants and an a/.alpha. diploid strain could not. Apparently, a cells have a mechanism, which may involve uptake or inactivation of .alpha. factor, for recovering from .alpha. factor arrest. The results do not distinguish between a recovery mechanism which is constitutive and one which is induced by .alpha. factor. The loss of .alpha. factor activity during recovery appeared to be primarily cell contact mediated, although an extracellular, diffusible inhibitor of .alpha. factor that is labile or that functions stoichiometrically was not ruled out.