Phosphorylation of Mg(2+)-dependent protein phosphatase alpha (type 2C alpha) by casein kinase II.

In this study we show that rat Mg(2+)-dependent protein phosphatase alpha (MPP alpha) expressed in Saccharomyces cerevisiae cells was phosphorylated on serine residues in vivo. The recombinant rat MPP alpha purified from Escherichia coli cells harboring an expression vector was phosphorylated in vitro by casein kinase II, but not by casein kinase I, to 1.5 mol phosphate per mol enzyme protein. Analysis by phosphopeptide mapping and amino acid analysis suggested that the sites of both in vivo and in vitro phosphorylation were the same and involved only serine residues. These results suggest that the rat MPP alpha expressed in yeast cells is phosphorylated by yeast casein kinase II in vivo. It is further proposed that the phosphorylation sites are located in the carboxyl terminal region of the enzyme molecule.