[Supranucleosomal levels of chromatin structure: a nucleodisome].

Dinucleosome periodicity of DNA fragmentation produced by DNAase I in nuclei of erythroid cells replacing its lysine-rich histone H1 by erythrocyte-specific fraction H5 has been electrophoretically investigated. It was found that the double-nucleosome repeat becomes more definite as the content of H5 increases. Electrophoretic analysis of DNA fragments generated by DNAse I reveals a "nucleodisome" structure of chromatin not only is condensed inactive nuclei of mature erythrocytes but also in chromatin of transcriptionally-active cells possessing a usual lysine-rich histone H1 such as rat thymus cells or CHO cell line. It seems that the nucleodisome structure is the specific feature of any chromatin. The nuclease of another specificity (DNAse II) is also able to reveal dinucleosome periodicity in chromatin of both erythrocytes and sea urchin sperm. Comparison of the results of DNA cutting in nuclei of these cells allows us to establish that the pattern of chromatin fragmentation by DNAses I and II is very similar, if not identical. On the basis of data obtained a mechanism of nucleodisome splitting off is suggested.