This protein functions as a dosage-dependent inducer in mitotic control. It is a tyrosine protein phosphatase required for progression of the cell cycle. It may directly dephosphorylate p34(cdc2) and activate the p34(cdc2) kinase activity. H2O + O-phospho-L-tyrosyl-[protein] = L-tyrosyl-[protein] + phosphate Belongs to the MPI phosphatase family.