ABSTRACT
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.
Subject(s)
Histones/analysis , Nucleosomes/ultrastructure , Animals , Chromatin/ultrastructure , DNA/analysis , DNA, Superhelical/analysis , L Cells/analysis , Mice , Micrococcal Nuclease , Molecular WeightABSTRACT
Chromosomal proteins were treated with imido esters or with formaldehyde. Histones and their oligomers were then obtained by acid extraction and analyzed by two-dimensional gel electrophoresis. We discovered a nonameric histone oligomer in which histone H1 complexes with the octamer of small histones. In this complex, H1 interacts preferentially with H2a and H3. One can suppose from these experiments that histone H1 has close contacts with core histones. Another conclusion from the results obtained is that the structure of the nucleosome core is different in H1-containing mononucleosomes and in core particles. Thus, histone H1 is an important component of the nucleosomal protein complex and its presence is necessary for supporting the native compact state of the nucleosomal core.
