Abstract
Chromatin was reconstituted from core histones and recombinant plasmid DNAs carrying poly(dA) . poly(dT) inserts of various lengths. A 97‐bp insert was found to occupy discrete and regularly‐spaced positions on the edges of the nucleosome. This insert cannot, however, be entirely included due to a block in the center of the particle. In contrast, nucleosomes reconstitute on a shorter 20‐bp insert. In this case, the insert shows a marked preference for the edges of the particle. Possible structural and physiological implications of these observations are discussed.