Complementary DNAs (cDNAs) of protein phosphatase 2C (PP2C) were cloned from two marine scuticociliates Uronema marinum and Miamiensis avidus. Both PP2C proteins showed structural characteristics of typical PP2C, such as highly conserved amino acid residues predicted for binding to phosphate and metal ions, 11 conserved PP2C motifs and 10 invariant residues. The phosphatase activity of recombinantly produced U. marinum PP2C (UmPP2C) was in proportion to the PP2C protein and Mg2+ concentrations, and was not sensitive to okadaic acid, but was inhibited by sodium fluoride, EDTA or Ca2+. The expression of UmPP2C was significantly up-regulated by exposure the ciliates with PMA suggesting that UmPP2C dephosphrylates proteins phosphorylated by protein kinases as in other eukaryotes and has a regulatory function against abrupt increase of protein phosphorylation triggered by strong stimulations.
