COMPARISON OF THE BIOCHEMICAL AND BIOLOGICAL FUNCTIONS OF TYROSINE PHOSPHATASES FROM FISSION YEAST, BUDDING YEAST AND ANIMAL-CELLS

In a previous communication, we have shown that two protein tyrosine p hosphatases (PTPases) from fission yeast, pyp1(+) and pyp2(+), act as novel inhibitors of mitosis upstream of the wee1(+) lmik1(+) pathway ( Ottilie et al., 1992). Here we describe that both genes possess intrin sic PTPase activity as judged by in vitro PTPase assays using P-32-lab eled Raytide as a substrate, and that P-32-labeled p107(wee1) is an in vitro substrate for pyp1. To compare the biological activity of pyp1 and pyp2 to that of other known PTPases, we expressed the budding yeas t PTP1 and human placental phosphatase 1B (PTP1B) genes in either a cd c25-22 or wee1-50 genetic backgound and established that, in contrast to pyp1(+) and pyp2(+), Saccharomyces cerevisiae PTP1 and human PTP1B complement the cdc25 mutant, opposing the weel( )+lmik1(+) pathway.