Nuclear protein kinases of GH3 cells.

Three distinct cAMP-independent nuclear protein kinase activities (PCV, PC-II and PC-III) have been separated by phosphocellulose chromatography of GH3 nuclear NaCl extracts. The kinase activities exhibit distinct substrate specificities and preference for either the basic substrates protamine sulfate and histones H1 and H3 (kinase activity PCV) or the acidic protein substrates casein (PC-II) and phosvitin (PC-III). The three nuclear protein kinases further differ in their estimated molecular weights, apparent Km values and in their sensitivity toward NaCl. All three kinases require Mg2+ for optimal activity.