Differential phosphorylation of high mobility group protein HMG 14 from calf thymus and avian erythrocytes by a cyclic GMP-dependent protein kinase

Phosphorylation of HMG 14 proteins from calf thymus and avian erythrocytes was studied using a cyclic GMP-dependent protein kinase from bovine lung. HMG 14 from calf thymus was a good substrate for the enzyme, but HMG 14 from avian erythrocytes was not phosphorylated. Of the potential phosphorylation sites, the one in the amino terminal sequence Pro-Lys-Arg-Lys-Val-Ser-Ser-Ala-Glu (residues 1–9) is present in HMG 14 from calf thymus but not in HMG 14 from avian erythrocytes suggesting that the phosphorylated amino acid residue in HMG 14 from calf thymus is Ser-6 (and possibly Ser-7).