Analysis of subunit organization in chicken erythrocyte chromatin.

Micrococcal nuclease digestion of intact chicken erythrocyte nuclei is shown to result in the formation of core nucleoprotein particles containing about 140 base pairs of DNA. These core particles, which are almost entirely devoid of histones f1 and f2c, are derived from transient nucleoprotein particles containing an average of approximately 180 base pairs of DNA. Oligomers of these latter particles may be isolated after brief nuclease digestion. The time course of digestion of these oligomers demonstrates the existence of "spacer" regions of more accessible DNA between core particles. Redigestion of purified monomer core nucleoprotein particles gives rise to both single-strand and double-strand DNA fragment patterns similar to those resulting from digestions of chromatin in situ. This observation indicates that the core particles we isolate are representative of nucleoprotein structures existing within the nucleus.