Aggregation of small oligonucleosomal chains into 300-A globular particles.

Chicken erythrocyte oligonucleosomes (trimers to about 20-mers) are able to interact with each other through the very lysine-rich histones (H1 and H5) and form heterogeneous globular particles with a mean diameter of about 300 A. These particles assemble spontaneously during micrococcal nuclease digestion of chromatin in the presence of 30 mM NaCl and contain approximately 25 nucleosomes. They are sensitive to ionic strength and unfold at lower salt concentrations but can be reconstituted by restoring the initial salt concentration. Even at 30 mM NaCl, the particles remain dynamic structures, being in equilibrium with their oligonucleosomal components as revealed by the fact that particle stability depends on the concentration of oligonucleosomes.