Effect of extraction of histones and their reconstitution on [3H] actinomycin D binding to isolated nuclei of the root of Pinus silvestris.

The purpose of the study presented was to investigate the effect of the extraction of histones on the template activity of DNA, measured by the autoradiographically evaluated intensity of [3H]actinomycin D ([3H]AMD) binding. The study was carried out on nuclei isolated from the root meristem of Pinus silvestris. Histones were removed selectively from them and reconstituted in the nuclei deprived of these proteins. The greatest rise in radioactivity was found after the extraction of the arginine fraction and that of lysine-rich and moderately lysine-rich fractions removed together, whereas the extraction of the lysine-rich fraction does not cause such a considerable increase in radioactivity. The reconstitution of particular histone fractions induced a fall in radioactivity to the level of controls in all the cases examined. No [3H]AMD binding to the nucleolus was found. The extraction of lysine histones results in the decondensation of chromatin and their reconstitution in the formation of complexes of compact chromatin.