[State of DNA slots in mono- and oligonucleosomes and in DNA complexes with individual histones]

The state of the major and the minor DNA grooves in purified mono- and oligonucleosomes and in the complexes of DNA with different histones have been studied by means of methylation of DNA with dimethyl sulphate. In nucleosomes histones shielded major groove by 18--20%. This result agrees well with our previous data obtained with chromatin, nuclei and whole cells. Each of the purified histones H2a, H2b, H3 and H4 as well as N-terminal peptides of H4 histone cause relative shielding of the DNA major groove by 15--18% like whole histone does. H1 histone protects neither DNA grooves from methylation. Our results suggest that histones are buried partly in the major groove of DNA in chromatin and purified nucleosomes. The arrangement of histones in the major groove does not depend probably on their specific organization in nucleosomes.