TI - Identification of the phosphoserine residue in histone H1 phosphorylated by protein kinase C . AB - The site -specific phosphorylation of bovine histone H1 by protein kinase C was investigated in order to further elucidate the substrate specificity of protein kinase C . Protein kinase C was found to phosphorylate histone H1 to 1 mol per mol . Using N-bromosuccinimide and thrombin digestions , the phosphorylation site was localized to the globular region of the protein , containing residues 71-122 . A tryptic peptide containing the phosphorylation site was purified . Modification of the phosphoserine followed by amino acid sequence analysis demonstrated that protein kinase C phosphorylated histone H1 on serine 103 . This sequence , Gly97-Thr-Gly-Ala-Ser-Gly-Ser (PO4) -Phe-Lys105 , supports the contention that basic amino acid residues C-terminal to the phosphorylation site are sufficient determinants for phosphorylation by protein kinase C .