The Selective Extraction of Histone Fractions from Deoxyribonucleoprotein

Three methods are described for quantitative depletion of calf thymus and chicken erythrocyte chromatin of various histone fractions. All methods involve dissociation of the histone fractions in question from chromatin in the presence of the ion‐exchange resin AG50W X 2 which, having strongly bound the free histones in solution, is easily removed from the chromatin. The depleted chromatins do not appear to be denatured. Method 1. In 0.45–0.65 M NaCl, 0.05 M sodium phosphate buffer pH 7.0, histone F1 is quantitatively and selectively removed from calf thymus chromatin. In 0.55–0.65 M NaCl, 0.05 M sodium phosphate buffer pH 7.0 and a limiting amount of ion‐exchange resin, histone F2C is quantitatively and selectively removed from chicken erythrocyte chromatin. Histone F1 can be quantitatively and selectively removed from chicken erythrocyte chromatin by repeated extraction with 0.5 M NaCl pH 7. By further depletion with resin in 0.55–0.65 M NaCl, 0.05 M sodium phosphate buffer pH 7.0, chicken erythrocyte chromatin can be quantitatively and selectively depleted in both histones F1 and F2C. Method 2. In 0.25–0.45M NaCl, 0.05 M sodium phosphate buffer, 4 M urea pH 7.0, histones F1, F2B and F2A2 are quantitatively and selectively removed from calf thymus chromatin. Method 3. In 0.35 M NaCl, 30% ethanol, 4 M urea pH 7.0, an almost complete removal of histones F2A1 and F2A2 from calf thymus chromatin is achieved. In 0.35 M NaCl, 300% ethanol, 5–6 M urea pH 7.0, histone F3 is removed as well.