NUCLEOSOME-ASSOCIATED PROTEIN-KINASES IN MURINE ERYTHROLEUKEMIA-CELLS

Chromatin subunits from murine erythroleukemia cells were prepared by a method which releases actively transcribing genes. Two casein kinase activities (CK1 and CK2) were isolated from these nucleosomes by gel nitration in 0.5 m NaCl. CK1 (Mr ~ 200,000) and CK2 (Mr ~ 35,000) were further purified by phosphocellulose chromatography and characterized with regard to several parameters which may regulate their activity in vivo. CK1 has an NaCl optimum of 0.14 m, utilizes GTP as phosphate donor ~25% as efficiently as ATP, and phosphorylates a discrete group of high molecular weight nonhistone proteins in the unfractionated chromatin starting material. CK2 has an NaCl optimum of 0.24 m, cannot utilize GTP, and modifies a different group of nonhistones. Both kinases are inhibited by concentrations of hemin (<50 μm) which efficiently induce globin gene expression in erythroleukemia cells. A histone kinase resolved during the gel filtration step is unaffected by hemin. An investigation of the mode of hemin inhibition reveals that CK1 and CK2 interact in different fashions with the inhibitor. © 1979.