A thermal denaturation study of chromatin and nuclease-produced chromatin fragments

Abstract

Calf thymus chromatin and nuclease-produced chromatin fragments were examined by thermal denaturation measurements. Native chromatin gave a series of distinct melting transitions at 64, 73, 79 and 85.degree. C in 0.25 mM EDTA pH 8. Treatments such as dialysis, mechanical shearing or sulfhydryl oxidation of histone H3 carried out on native chromatin significantly altered the derivative melting profiles by blurring distinct transitions and shifting the highest melting transition to a lower temperature. Derivative melting profiles for electrophoretically purified chromatin fragments, monomer through hexamer, resembled that of dialyzed chromatin. Higher order structures probably exist in chromatin that are eesily disrupted. Since products of micrococcal nuclease (EC 3.1.4.7) digestion of the altered chromatins did not exhibit any major electrophoretic differences from those obtained from nuclei, then the primary arrangements of histones along the DNA are probably the main determinant for cleavage sites.