Purification and Characterization of a Specific Histone Hl Protein Kinase from Mouse Plasmacytoma

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Abstract
A protein kinase with high specificity for histone H1 was purified from a plasmacytoma microsomal fraction by a high-salt wash, ammonium sulfate precipitation and chromatography on DEAE-cellulose, hydroxyapatite and Sephadex G-200 columns, and the main properties of this kinase were studied. A sulfhydryl compound such as 2-mercaptoethanol or dithiothreitol was necessary for full activity. The optimum pH was 7.4-7.8. After purification the histone H1 kinase was not stimulated by cAMP or cGMP. It was not inhibited by the heat-stable cAMP-dependent protein kinase inhibitor from beef heart. It utilized preferentially GTP over ATP as phosphate donor. Km values for ATP and GTP were 58 and 1.4 .mu.M, respectively; the Km for histone H1 was 14 .mu.g ml-1. The MW was .apprx. 90,000 by gel-exclusion chromatography. Analysis of the purified H1-specific protein kinase by polyacrylamide gel electrophoresis in dodecylsulfate showed 2 bands having MW of .apprx. 64,000 and 54,000. Many characteristics of this kinase were similar to those of the chromatin-bound protein kinase reported in rapidly proliferating cells.