Chromatin accessibility to DNA minor groove ligands in vitro: role of linker histones and amino-terminal domains of octamer histones.

Using the circular dichroism spectra, induced in the visible range by the binding of minor groove ligands to DNA, we found that two drugs, DAPI and Hoechst 33258, are able to occupy their specific sites even when these are located inside the nucleosome structure. This high accessibility of the binding sites in the nucleosome is not modified by the removal of the amino-terminal domains of the octamer histones and, surprisingly, it is not reduced by the presence of linker histone. Interesting and reasonable differences were found in the association constants, that reveal the "reluctance" of the ligands to bind the DNA-minor groove when the histones are present.