Association of tissue-specific histones with deoxyribonucleic acid. Thermal denaturation of native, partially dehistonized, and reconstituted chromatins.

First derivative thermal denaturation profiles were compared for chromatin samples prepared from chicken erythrocytes, chicken liver, and sea urchin (Strongylocentrotus purpuratus) sperm. Selective dissociation of various histone fractions, including tissue-specific F2c and gamma histones, was manifested in characteristic changes of the thermal denaturation profiles. It was concluded that the binding of individual histone fractions to the DNA can be identified with paricular temperatures of thermal denaturation. This observation was tested by denaturation experiments on hybrid chromatins. Chicken erythrocyte chromatin devoid of F2c histone and reconstituted with isolated liver F1 histone denatured like chicken liver chromatin. Conversely, chicken liver chromatin devoid of F1 histones and reconstituted with isolated F2c fraction exhibited a thermal denaturation profile characteristic of the chicken erythrocyte chromatin. In other words, the thermal denaturation profile of reconstituted chromatin was determined approximately by the sum of contribution histone fractions. The obvious distinctions recognized among the derivative thermal denaturation profiles of compositionally different nucleoproteins suggest that thermal denaturation sensitively detects variations in histone content and therefore is a valuable tool for the routine characterization of chromatin preparations.