Highly specific phosphatase involved in the metabolism of ADP-ribose 1''-phosphate (Appr1p) which is produced as a consequence of tRNA splicing. Removes ADP-ribose from glutamate residues in proteins bearing a single ADP-ribose moiety. Inactive towards proteins bearing poly-ADP-ribose. ADP-beta-D-ribose 1''-phosphate + H2O = ADP-D-ribose + phosphate Optimum pH is 6.0. Present with 1170 molecules/cell in log phase SD medium. Belongs to the POA1 family.