An RGS protein regulates the pheromone response in the fission yeast Schizosaccharomyces pombe

The rate and extent of a cell's response to an extracellular stimulus is in fluenced by regulators that act on the intracellular signalling machinery. Although not directly involved in propagating the intracellular signal, reg ulators control the activity of the proteins that transmit the signals. To understand this aspect of cell signalling, we have studied the pheromone re sponse pathway in the fission yeast Schizosaccharomyces pombe, a relatively simple signalling system in a genetically tractable organism. We demonstra te this approach by investigating the role of Rgs1, a member of the Regulat or of G protein Signalling (RGS) family of proteins. The rgs1 gene was iden tified through the St. pombe genome sequencing project (accession number Q0 9777) and recognized as having similarity to RGS proteins [Tesmer ef al. (1 997) Cell 89: 251-261], but this is the first report concerning the activit y of the protein. Strains lacking rgs1 (Delta rgs1) are hypersensitive to p heromone stimulation and unable to conjugate with a mating partner. Inhibit ion of mating occurs at a relative late stage in the process as Delta rgs1 strains exhibit pheromone-dependent transcription and form shmoos. Expressi on of SST2 (an RGS protein that regulates pheromone signalling in the buddi ng yeast Saccharomyces cerevisiae) overcomes the hypersensitivity of the De lta rgs1 strains but fails to rescue their mating defect.