Protein phosphatase which seems to be involved in larval development but not essential for embryogenesis. 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. Serine/threonine-protein phosphatase 4 (PP4) occurs in different assemblies of the catalytic and one or more regulatory subunits. Belongs to the PPP phosphatase family. PP-4 (PP-X) subfamily.