We previously identified two genes, mfm1 and mfm2, with the potential to encode the M-factor mating pheromone of the fission yeast Schizosaccharomyces pombe (J. Davey, EMBO J. 11:951-960, 1992), but further analysis revealed that a mutant strain lacking both genes still produced active M-factor. Here we describe the isolation and characterization of a third M-factor gene, mfm3. A mutant lacking all three genes fails to produce M-factor, indicating that all functional M-factor genes now have been identified. The triple mutant exhibits an absolute mating defect in M cells, a defect that is not rescued by addition of exogenous M-factor. A mutational analysis reveals that all three mfm genes contribute to the production of M-factor. Their transcription is limited to M cells and requires the mat1-Mc and ste11 gene products. Each gene is induced when the cells are starved of nitrogen and further induced by a pheromone signal. Additionally, the signal transduction machinery associated with the pheromone response is required for transcription of the mfm genes in both stimulated and unstimulated cells.
Isolation and characterization of genes encoding two chitinase enzymes from Serratia marcescens
