Isotonic salt extract of nuclei of human tonsillar lymphocytes contained about 60-65% of the total histone kinase activity (EC 126.96.36.199) of the cells. The nuclear histone kinase activity was apparently cyclic AMP independent, although 20-25% of the total cyclic AMP-binding capacity of the cells was present in the nuclear extract. A cyclic AMP-dependent kinase (I), and an independent kinase (II), similar to those found previously in the hypotonic extract of the cells, were demonstrated in the nuclear extract by DEAE-cellulose chromatography. In addition a second type of cyclic AMP independent histone kinase (III) was found. On the basis of its catalytic properties, (kinetic parameters and the phosphorylation site of F2b histone), kinase III differed from kinase II, but it was similar to kinase I. Kinase III may be identical with the catalytic subunit of the cyclic AMP dependent enzyme. A cyclic AMP-binding fraction accompanied by a negligible amount of kinase activity was also demonstrated in the nuclear extract by DEAE-cellulose chromatography.
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