Histones can be extracted from chicken erythrocyte chromatin with 2 M CaCl2 10 mM Tris (pH 7.4). The core histones so extracted exist as H3–H4 tetramers and H2A–H2B dimers since calcium at >0.5 M result in dissociation of the histone octamer. Reconstitution of octamers occurs on removal of the Ca2+ by dialysis. Although <0.5 M calcium do not result in octamer dissociation, perturbations in the structure can be detected by CD and tyrosine fluorescence spectroscopy.
