ras1 and pat1 alleles interact to quantitatively and qualitatively alter conjugation in fission yeast

To identify novel components of ras1+ signalling in Schizosaccharomyces pombe, extragenic suppressors of the mating defect of ras1 effector mutants were isolated. A novel allele of pat1, pat1-e1, was isolated that increases the mating of ras1-D43E mutants to near wild-type levels but does not suppress the mating defect of ras1-I41M, ras1-Y37F, or ras1-Y45I mutants. This allele-specific suppression is not a characteristic of all pat1 alleles since pat1-3 and pat1-114 partially and equally suppress ras1-D43E and ras1-I41M mutants. Analysis of mating cultures showed that ras1-D43E and pat1-e1 interact to qualitatively alter the mating response. While pat1-e1 ras1-D43E cells were delayed in agglutination, cell-cycle delay, and mat1-Pm transcription, they induce mat1-Mc at the same time and mate more rapidly than other mating cultures. These results suggest that pheromone signalling, but not nutritional signalling, is delayed in pat1-e1 ras1-D43E cells. We hypothesize that this delay causes an elevated pheromone response and thus suppression of the mating defect of the ras1-D43E mutant by pat1-e1.