Analysis of DNA of isolated chromatin subunits.

Partial digestion of rat liver nuclei with staphylococcal nuclease results in the liberation of nucleo-protein complexes consisting of one or more upsilon bodies. By velocity centrifugation we have isolated the monomeric subunit in relatively pure form. We find that this subunit contains 185 base pairs of DNA and 240,000 daltons of protein, resulting in a protein to DNA ratio identical to that of unperturbed chromatin. The isolated monomeric particle is further susceptible to internal nuclease attack resulting in the solubilization of 46% of the monomeric DNA. Analysis of the resistant DNA reveals a complex but highly reproducible pattern of DNA fragments ranging from 160 to 60 base pairs in length. Analysis of the reassociation kinetics of the isolated subunit DNA reveals that most, if not all genomic sequences, are involved in this basic subunit structure. No special frequency class of DNA is absent from upsilon bodies. Furthermore, virtually all liver sequences transcribed into mRNA are present in upsilon body DNA. These results indicate that upsilon body formation may be random with respect to DNA sequence and suggest that the mere presence of upsilon bodies over a specific region of DNA is not sufficient to restrict its transcription.