Phosphorylation of Histone H2A by Protein Kinase C and Identification of the Phosphorylation Site

Abstract

In regenerating rat liver, nuclear protein histone H2A was shown to be phosphorylated on its amino-terminal serine residue [Sung et al. (1971) J. Biol. Chem. 246, 1358-1364], but the protein kinase which phosphorylates this residue has not been identified. To evaluate the possibility that protein kinase C can phosphorylate this residue, calf thymus histone H2A was ³²P-labeled by incubation with [γ-³²P] ATP and highly purified protein kinase C from rat brain in the presence of calcium and phospholipid. About 1 mol of ³²P was incorporated per mol of histone H2A and the K_m and apparent V_max of the reaction were calculated to be 2.1μM and 0.35μmol/min/mg, respectively. So histone H2A seemed to be a good substrate for protein kinase C. Further, the proteolytic phosphopeptides of ³²P-labeled histone H2A were isolated by means of a series of column chromatographies and analyzed for their amino acid compositions. Comparison of the data with the known primary structure of histone H2A revealed their amino acid sequence as ¹Ser-Gly-Arg. These data suggest that protein kinase C may be a candidate for the protein kinase which phosphorylates the amino-terminal serine residue of histone H2A during the regeneration of rat liver.