Two chromatin fractions with different metabolic properties of non-histone proteins and of newly synthesized RNA.

Digestion of chromatin with micrococcal nuclease under mild conditions results in the release of a minor chromatin fraction showing an increased RNA and non-histone protein content, a fast turnover of the non-histone proteins and the presence of rapidly labelled heterogeneous nuclear RNA (hnRNA) with half-life of about 20 min. Further digestion of the chromatin leads to the elimination of about 19% of the initial chromosomal DNA, thus leaving a second chromatin fraction relatively resistant to nuclease attack. This fraction has a low protein and RNA content and contains only metabolically stable non-histone proteins. No differences in the histone complement of the two fractions was found except for a 40% deficiency of H1 in the minor fraction.