Abstract
The interactions were studied of DNA with the nonhistone chromatin protein HMGB1 and histone H1 in the presence of manganese(II) ions at different protein to DNA and manganese to DNA phosphate ratios by using absorption and optical activity spectroscopy in the electronic [ultraviolet (UV) and electronic circular dichroism ECD)] and vibrational [infrared (IR) and vibrational circular dichroism (VCD)] regions. In the presence of Mn^2+^, the protein–DNA interactions differ from those without the ions and cause prominent DNA compaction and formation of large intermolecular complexes. At the same time, the presence of HMGB1 and H1 also changed the mode of interaction of Mn^2+^ with DNA, which now takes place mostly in the major groove of DNA involving N~7~(G), whereas interactions between Mn^2+^ and DNA phosphate groups are weakened by histone molecules. Considerable interactions were also detected of Mn^2+^ ions with aspartic and glutamic amino acid residues of the proteins. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 182–192, 2006
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