Isopycnic banding of chromatin in chloral hydrate gradients

Chromatin from Ehrlich ascites tumor cells bands in chloral hydrate gradients at densities ranging from 1.40 to 1.60 g/cm³. The total chromatin after recovery from the gradient has a composition similar to that of native chromatin. Chloral hydrate does not dissociate the chromatin into its nucleic acid and protein components. The chloral hydrate is inert toward both the DNA and the histone, as indicated by the lack of influence either on the melting curves of the DNA, or on the electrophoretic patterns of the histones, when these substances are recovered from chromatin treated with chloral hydrate. The resolution of chromatin on the gradients reflects different buoyant densities of the chromatin, and this in turn, different protein to DNA ratios. Extraction of the histones from chromatin obtained from different regions of the gradients reveals differences in prevalence of at least two of the histone species, and provides evidence suggesting that different stretches of DNA in the genome may associate with different histones.