Danger of Contamination in Chromatographically Prepared Arginine-rich Histone

Cell nuclei prepared from mammary gland were contaminated to various extents with cytoplasm. Histones extracted by acid from such nuclear preparations contained nonhistone protein, the amount of which increased dramatically as cytoplasmic contamination increased. Reasonably pure nuclei could be obtained by sedimentation through dense sucrose or treatment with detergent. Even when these purified nuclei were used, the arginine-rich histone prepared by elution from Amberlite IRC-50 with guanidinium chloride contained contaminants which could be detected and measured by amino acid analysis. The contamination was substantially reduced by modifying the histone isolation procedure to include stepwise extraction at decreasing pH values or prior treatment of the crude deoxyribonucleoprotein with organic solvents.