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).