Nucleic Acids Research, 1978, Vol. 5, No. 3 739-750
© 1978
Articles |
Fractionation of chromatin by differential solubility in dilute salt
Paterson Laboratories, Christie Hospital and Holt Radium Institute Manchester M20 9BX The Beatson Institute for Cancer Research, Wolfson Laboratory for Molecular Pathology Garscube Estate, Switchback Road, Bearsden, Glasgow, UK
Received December 13, 1977. Chromatin prepared from the livers of rats was fractionated on the basis of solubility in dilute NaC1. Neither of the fractions obtained was enriched in newly synthesized DNA. The salt-soluble fraction had a higher protein content (usually up to 50%) relative to the DNA, and contained 72% or more of the rapidly synthesized RNA. This RNA was found to be complexed with the salt-soluble deoxyribonucleoprotein, not merely co-solubilized with it. Also, polylysine-binding studies showed that about 70% or more of the nucleic acid phosphates were accessible as compared to about 40% in the unfractionated chromatin. These properties suggested that the soluble fraction was enriched in actively transcribed chromatin. In contrast molecular hybridization studies showed that the complexity of the DNA and its homology with cDNA transcribed from rat-liver polysomal mRNA were the same as those of DNA from unfractionated chromatin, or from the salt-insoluble fraction. This suggests that the criteria commonly accepted as distinguishing between euchromatin and heterochromatin in vitro are not invariably valid.