Ca2+ signal is generated only once in the mating pheromone response pathway in Saccharomyces cerevisiae

The mating pheromone, alpha-factor, of the yeast Saccharomyces cerevisiae b inds to the heterotrimeric G protein-coupled cell surface receptor of MATa cells and induces cellular responses necessary for mating. In higher eukary otic cells, many hormones and growth factors rapidly mobilize a second mess enger, Ca2+, by means of receptor-C protein signaling. Although striking si milarities between the mechanisms of the receptor-G protein signaling in ye ast and higher eukaryotes have long been known, it is still uncertain wheth er the pheromone rapidly mobilizes Ca2+ necessary for early events of the p heromone response. Here we reexamine this problem using. sensitive methods for detecting Ca2+ fluxes and mobilization, and find no evidence that there is rapid Ca2+ influx leading to a rapid increase in the cytosolic free Ca2 + concentration. In addition, the yeast PLC1 deletion mutant lacking phosph oinositide-specific phospholipase C, a hey enzyme for generating Ca2+ signa ls in higher eukaryotic cells, responds normally to the pheromone. These fi ndings suggest that the receptor-G protein signaling does not utilize Ca2as a second messenger In the early stage of the pheromone response pathway, Since the receptor-G protein signaling does stimulate Ca2+ influx after ea rly events have finished and this stimulation is essential for late events in the pheromone response pathway {Iida et al,, (1990) J, Biol, Chem., 265: 13391-13399} Ca2+ may be used only once in the signal transduction pathway in unicellular eukaryotes such as yeast.