Protein kinase activity can be separated from the purified activated rat liver glucocorticoid receptor.

Previous studies have shown that the purified rat liver glucocorticoid receptor (GR) has a protein kinase activity. In this report we show that the GR-associated kinase can be partially separated from the 94-kDa steroid-binding protein by DEAE-Sepharose chromatography. The kinase elutes from the column at a higher salt concentration than the 94-kDa GR protein. This GR copurifying protein kinase phosphorylates basic substrates such as various histone fractions and protamine. The phosphorylation occurs in the presence of Mg2+ ions, and is not supported by Ca2+ ions. The amino acid residues phosphorylated by the kinase are threonine and serine. This kinase also phosphorylates the 94-kDa GR protein and thus might be of physiological relevance for the GR function.