Isolation and physical characterization of a stable core particle.

Core particles were prepared from mature chicken erythrocytes chromatin, according to the method of Lutter (J. Mol. Biol. 124, 391, 1978) with one major modification: after the second digestion, zonal centrifugation was used to isolate the core particle, instead of chromatography on Sepharose 6B. By using circular dichroism and electron microscopy, we were able to follow each step of the preparation and to offer an explanation of the discrepancies found in previous preparations and in our own preparations.