Fractionation of chromatin by differential solubility in dilute salt

Abstract

Chromatin prepared from the livers of rats was fractionated on the basis of solubility in dilute NaCl. 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 activity 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.

Role of histone H1 in the conformation of oligonucleosomes as a function of ionic strength

“…It may be excluded, however, that this fraction would be the actively transcribed portion of chromatin. Hybridization studies with cDNA transcribed frorti liver polysomal mRNA have shown that the fraction of chromatin most readily digestible with micrococcal nuclease is not enriched in active chromatin (Itzhaki et al, 1978). Secondly, the isolated oligonucleosomes were not remarkable with respect to protein composition (cf.…”

“…This may indicate that one deals with a special portion of chromatin. On the other hand, there are reports on salt-soluble oligonucleosomes(Itzhaki et al, 1978;Campbell & Cotter, 1977;Wittig & Wittig, 1977;Whitlock & Simpson, 1976;Renz et al, 1977;Lewis et al, 1976; Stratling et al, 1978a,b). Also, the "solubility" of oligonucleosomes depends on the chromatin concentration and the chain length(Campbell & Cotter, 1977; Wittig& Wittig, 1977).…”