[Study of fractionated rat liver and sea urchin chromatin]

Two chromatin fractions were isolated from rat liver nuclei and from sperm of the sea urchin, Strongylocentrotus intermedius, by chromatin treatment with DNAase II with subsequent fractionation of the resultant fragments via their precipitation with MgCl2 solution. The analysis of distribution between these fractions of rapidly in vivo labeling RNA associated with chromatin and the in vitro investigation of template activity of isolated chromatin fractions allowed to conclude that one of the fractions is transcriptionally active and the other is inactive. The active chromatin fraction, similarly to the inactive one, contains all five histones. Unlike the latter, however, the former fraction is enriched in non-histone proteins and impoverished in histone H1. It is shown that the active chromation fraction of rat liver is composed of small fragments heterogenous in size. Rapidly synthesizing RNA in this fraction is mainly associated with mononucleosomal particles. Data on electrophoretic mobility of DNA fragments isolated from the active chromatin fraction from rat liver show that transcriptionally active sites of chromatin retain the nucleosomal structure.