GENETIC-ANALYSIS OF THE SAM MUTATIONS, WHICH INDUCE SEXUAL DEVELOPMENT WITH NO REQUIREMENT FOR NUTRITIONAL STARVATION IN FISSION YEAST

The cAMP pathway and the Ras pathway are the two major pathways to sex ual development in the fission yeast Schizosaccharomyces pombe. To und erstand the cAMP pathway or the related pathway, we analyzed mutants t hat display a phenotype similar to cyr1(-), that is, hyper-sporulation . Nine mutants termed sam (sporulation abnormal mutant), which are hig hly inclined to sexual development despite the presence of nitrogen so urces, were partially characterized. Cyclic AMP was detected in all ni ne sam mutant cells, and over-expression of the adenylyl cyclase gene (cyr1) failed to suppress the hyper-sporulation phenotype of these sam mutants, suggesting that none of the sam mutants were likely to be al lelic to cyr1. Epistatic tests of sam mutants showed that they mere di vided into two dominant and seven recessive mutants. Dominants mere ab le to make spores in sam/sam(+) heterodiploid cells upon abundant nutr ients. Both two dominant mutants bypassed the inability to make spores in ras1 deficient diploid cells, suppressed the deficiency to execute sporulation in byr2 deficient diploid cells, but failed to suppress t he byr1 deficiency. Two dominant mutations seem not to occur within th e byr2 gene.