EXPRESSION, PURIFICATION AND KINETIC-BEHAVIOR OF FISSION YEAST LOW M(R) PROTEIN-TYROSINE-PHOSPHATASE

A gene named stp1(+), coding for a 17.5-kDa protein, that rescues cdc2 5-22 when overexpressed, has been previously isolated from fission yea st, Here we describe the expression and purification of Stp1 protein a s a fusion with the glutathione S-transferase in E. coli and its kinet ic characterisation. Stp1 deduced protein sequence shows an high homol ogy to members of a class of cytosolic low M(r) protein phosphatase pr eviously known to exist only in mammalian species. Stp1 has a kinetic behaviour that appears to be intermediate with respect to the two isoe nzymatic forms of low M(r) protein tyrosine phosphatases present in ma mmalian tissues. These differing kinetic characteristics are mainly du e to the sequence 45-56 that is spatially close to the active site poc ket.