We have purified and characterised an apparently novel nuclear 42-kDa casein kinase from epithelial cells of Chironomus tentans which comigrates with a phosphoprotein associated with transcriptionally active salivary gland genes. The protein kinase promotes phosphorylation of casein and phosvitin, using either ATP or GTP as phosphate donors, and undergoes autophosphorylation. The casein kinase activity of the 42-kDa protein sensitive to heparin, 5,6-dichloro-1-β-d-ribofuranosylbezimidazole (DRB), spermine and spermidine indicating that it is a novel enzyme with similar but not identical properties to casein kinase II or nuclear protein kinase NII.
