Localization of chromatin proteins within DNA grooves by methylation of chromatin with dimethyl sulphate

The use of the comparative modification with ³H-dimethyl sulphate (DMS) of free DNA and DNA in different complexes is proposed to evaluate the shielding of the minor and major grooves of the DNA double helix and to determine the presence of single-stranded DNA in the complexes.Glucosyl groups in DNA of T6 phage protect, as expected, the major groove, and actinomycin d in its complex with DNA shields the minor groove against methylation with DMS.The data obtained suggest that histones and protamine in reconstituted nucleohistone and nucleoprotamine are allocated within partly the major groove leaving the minor groove open, while polylysine does not seem to be buried within either of the grooves, and cations of cetyltrimethylammonium lie within the minor groove of DNA.