mop, Ptp36E and Pez are predicted to encode pseudophosphatases, and the mop and Pez products do not show detectable phosphatase activity in vitro (FBrf0227974, FBrf0220289). These genes are therefore omitted from this group.

primo-1 is predicted to be a pseudophosphatase in FBrf0227974, but FBrf0247574 shows that it does have protein tyrosine phosphatase activity, and so it is included in this group.

primo-1, primo-2 and CG14297 are 'low molecular weight protein tyrosine phosphatases' and are included in the CYTOSOLIC PROTEIN TYROSINE PHOSPHATASES gene group. They have limited sequence similarity to the PTP family, but possess the Cys-X5-Arg active-site signature motif. (FBrf0227974 provides an alternative classification.) Argp is also a 'low molecular weight protein tyrosine phosphatase' but it has been demonstrated to have protein arginine phosphatase activity (FBrf0247574).