MUTATIONS IN CYR1 AND PAT1 REVEAL PHEROMONE-INDUCED G(1) ARREST IN THE FISSION YEAST SCHIZOSACCHAROMYCES-POMBE

Investigations into sexual differentiation and pheromone response in t he fission yeast Schizosaccharomyces pombe are complicated by the need to first starve the cells of nitrogen. Most mating-related experiment s are therefore performed on non-dividing cells. Here we overcome this problem by using two mutants that bypass the nutritional requirements and respond to the M-factor mating pheromone in rich medium. The firs t mutant lacks the cyr1 gene which encodes adenylate cyclase and these cells contain no measurable amounts of cAMP. When M-factor is added t o a growing h(+) cyr1(-) strain it causes a transient G(1) arrest of c ell division, transcription of mat1-Pm, and elongation of the cells to form shmoos. The second mutant contains the temperature-sensitive pat 1-114 allele. At 30 degrees C this mutant was previously shown not onl y to by pass the nutritional signal but also to stop growing in a stat e derepressed for pheromone-controlled functions. We now report that a n h(+) pat1-114 strain growing mitotically at 23 degrees C responds to M-factor. This shows that the pat1 protein kinase can be tuned to der epress nutritional signalling while repressing the other stages in the differentiation process.