Self-assembly of single and closely spaced nucleosome core particles

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Abstract
Self-assembly of DNA with the four core histones but in the absence of H1 generates nucleosome core particles which are spaced randomly over large distances. Closely spaced core particles, however, exhibit a preferred short linkage which is not a multiple of 10 base pairs. They bind about 140 base pairs whereas apparently shorter DNA lengths per nucleosome observed after digestion with micrococcal nuclease are the result of degradation from the ends. The DNA length of one superhelical turn in the core particle is 83 ± 4 base pairs. Single core particles may bind more DNA than closely spaced core particles but probably less than two full turns or 168 base pairs . The internal structures of single and of native core particles are very similar as judged by their amount of DNA, sedimentation coefficient, appearance in the electron microscope, and digestion with DNase I. In addition to core particles, a particle is described which sediments at 9 S and consists of 108 base pairs of DNA bound to the histone octamer. It appears to be the smallest stable “core particle” but it is not a degradation product of the 146-base-pair core particle. Digestion of end-labeled 9 S and nucleosome core particles with DNase I shows distinct differences.