The fission yeast genes pyp1⁺ and pyp2⁺ encode protein tyrosine phosphatases that negatively regulate mitosis

We have used degenerate oligonucleotide probes based on sequences conserved among known protein tyrosine phosphatases (PTPases) to identify two Schizosaccharomyces pombe genes encoding PTPases. We previously described the cloning of pyp1⁺ (S. Ottilie, J. Chernoff, G. Hannig, C. S. Hoffman, and R. L. Erikson, Proc. Natl. Acad. Sci. USA 88:3455-3459, 1991), and here we describe a second gene, called pyp2⁺. The C terminus of each protein contains sequences conserved in the apparent catalytic domains of all known PTPases. Disruption of pyp2⁺ results in viable cells, as was the case for pyp1⁺, whereas disruption of pyp2⁺ and pyp1⁺ results in synthetic lethality. Overexpression of either pyp1⁺ or pyp2⁺ in wild-type strains leads to a delay in mitosis but is suppressed by a wee 1-50 mutation at 35°C or a cdc2-1w mutation. A pyp1 disruption suppresses the temperature-sensitive lethality of a cdc25-22 mutation. Our data suggest that pyp1⁺ and pyp2⁺ act as negative regulators of mitosis upstream of the weel ⁺/mik1⁺ pathway.