Forms the histone H2A phosphatase complex in association with the regulatory subunits PSY2 and PSY4, which dephosphorylates H2AS128ph (gamma-H2A) that has been displaced from sites of DNA lesions in the double-stranded DNA break repair process. Dephosphorylation is necessary for efficient recovery from the DNA damage checkpoint (By similarity). H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 2 manganese ions per subunit. Catalytic subunit of the histone H2A phosphatase complex (HTP-C) containing PPH3, PSY2 and PSY4. Belongs to the PPP phosphatase family. PP-4 (PP-X) subfamily.