Effects of Heparin and Polyamines on the Phosphorylation of High Mobility Group Proteins by Cyclic Nucleotide-Independent Phosvitin Kinase from Pig Testis

Abstract

In order to study the physiological role played by cyclic nucleotide-independent phosvitin kinase in pig testis, effects of heparin (an inhibitor of RNA synthesis) and polyamines (stimulators of the synthesis) on the enzyme, distribution in nuclei of the enzyme, and identification of endogenous substrates for the enzyme were examined. The enzyme was shown to be inhibited by heparin, nd the inhibition was removed by the addition of polyamines, when phosvitin (the best exogenous substrate for the enzyme) was used as substrate. The inhibition by heparin and inhibition removal by polyamines was dependent on Mg2+ concentration. The enzyme was found to be present in pig testis nuclei as well as in the cytosol. The enzyme phosphorylated chromatin-associated non-histone proteins in the testis nuclei. Of the non-histone proteins, high mobility group (HMG) 14 and 17 were identified as substrates for the enzyme. Phosphorylation of HMG 14 and 17 was also inhibited by heparin and inhibition of HMG 14 phosphorylation was removed by the addition of polyamines, although the effect was less dependent on Mg2+ concentration. These results suggested that phosvitin kinase was involved in the regulation of RNA synthesis int he testis.