Polyamines and heparin do not appreciably influence phosphorylation of chromatin proteins HMG 14 and HMG 17 by nuclear protein kinase II

Phosphorylation of acidic substrates such as casein and phosvitin by nuclear protein kinase II is stimulated by polyamines and inhibited by heparin, which mimics an endogenous proteoglycan inhibitor. The phosphorylation in vitro of the chromatin proteins HMG 14 and HMG 17 by nuclear protein kinase II were examined in this study focusing on the modifying effects of polyamines and heparin. Both HMG proteins were phosphorylated by the enzyme, but polyamines did not appreciably influence the extent of their phosphorylation. In addition, heparin did not inhibit the kinase reaction with the HMG proteins as substrates. These results indicate that the nuclear protein kinase II does actively phosphorylate HMG 14 and HMG 17 in vitro but that in contrast to some model substrates, polyamines and heparin do not appreciably affect their phosphorylation.