[Splitting of mononucleosomes into histone-containing subnucleosomes].

Histone-containing subnucleosomal particles SN7 and SN4 revealed initially in micrococcal nuclease digest of mouse chromatin were studied. It was found that production of SN7 and SN4 did not depend on the preservation of supranucleosomal levels of chromatin organization and was the result of intranucleosomal splitting. Micrococcal nuclease that preferentially attacks internucleosomal linker DNA can cut mononucleosomes with the formation of 40 b. p. DNA fragment complexed with H2a and H2b and SN7 particle containing six histones (H2a, H2b, 2H3 and 2H4) and 108 b. p. DNA. It is proposed that such a splitting of nucleosomes reflects their intimate organization, particularly a histone-DNA interaction within core particles. These results are interpreted in terms of a nucleosomal model in which H2a-H2b pairs are localized in the peripheral parts of the nucleosomal DNA superhelix.