Fractionation of chromatin, released by nuclease digestion, on ECTHAM-cellulose. Separation of active and inactive chromatin.

Chromatin released by two nucleases under various ionic conditions has been fractionated by chromatography on ECTHAM-cellulose. Mg2+ -soluble chromatin, which according to Gottesfeld and Partington is enriched in transcribed DNA sequences (Gottesfeld, J.M. and Partington, G.A., (1977) Cell 12, 953-962) and produced by DNAase II digestion at intermediate ionic strength, comprises material eluting from ECTHAM-cellulose at 80-100 mM Cl-, pH 6.8-7.0, whereas bulk, Mg2+ -insoluble chromatin comprises more tightly binding material. Free hnRNP particles elute at 30 mM Cl-, pH 6.8. Oligonucleosomes, which according to Dimitriadis and Tata are enriched in transcribed sequences (Dimitriadis, G.J. and Tata, J.R. (1980) Biochem. J. 187, 467-477) and produced by micrococcal nuclease digestion at physiological ionic strength, also elute predominantly at 80-100 mM Cl-, pH 6.8-7.0. When liver nuclei are digested with micrococcal nuclease at low ionic strength, the most rapidly released chromatin is enriched in nascent RNA and hnRNP particles, and binds weakly to ECTHAM-cellulose. More slowly solubilised chromatin, containing fewer hnRNP particles, binds much more strongly to ECTHAM-cellulose. In confirmation of results with mechanically sheared chromatin, the affinity of particular chromatin fractions is not dependent on the size of chromatin particles, rather it reflects the differing composition, and in particular the non-histone protein and hnRNP content, which, we propose, determines the conformation adopted by different chromatin fractions in the cation conditions used for elution from ECTHAM-cellulose.