Binding of polylysine and ethidium bromide to nucleosomal DNA: comparison of biochemical and electron microscopical results.

Ethidium bromide and polylysine interact with nucleosomal DNA and lead to change of biochemical properties and to morphological changes as to the distance between the two core particles of a nucleosome dimer. With increasing polylysine concentration, the buoyant density of nucleosomes decrease and the accessibility of the nucleosomal DNA to micrococcal nuclease is lowered. Electron microscopy of polylysine treated nucleosome dimers reveals a shortening of the internucleosomal distance as compared with controls. Treatment of nucleosomes with ethidium bromide leads to an enhanced accessibility of the nucleosomal DNA to micrococcal nuclease. Electron microscopy reveals an increase in length of the DNA connecting the two nucleosome cores in the presence of the dye. Both the binding of polylysine and the treatment with ethidium bromide apparently do not affect the histone arrangement within the nucleosome core as suggested by chemical cross-linking of histones and DNA with formaldehyde, and no obvious morphological change of the nucleosome cores can be observed.