volumes no.n N o v e m b e r ^ Nucleic Acids Research Stability of nucleosomes in native and reconstituted chromatins.

The stability of nucleosomes of SV4 0 minichromosomes extracted from infected cells or reconstituted by association of SV4 0 DNA and the four histones H2A, H2B, H3 and H4 was studied as a function of the ionic strength. As a measure of the stability of the nucleosome, we followed the disappearance of the nucleosomes from the original chromatin and their appearance on a "competing " DNA. We show here that the DNA and the histone components of the nucleosomes do not apprecially dissociate below 8 00 mM NaCl. At 8 00 mM and above, the histone moiety of the nucleosomes can dissociate from the DNA and efficiently participate to the formation of nucleosomes on a "competing " DNA