Structural properties of barley nucleosomes

Linear dichroism spectroscopy of nucleic acids

“…Because of the requirement of low conductivity in electric field orientation, in most of the early ELD studies the chromatin was condensed by di-and multivalent cations, and under these conditions, positive dichroism of condensed chromatin was not observed. However, chromatin condensed with monovalent cations has positive dichroism under all conditions, independently of orientation technique (Lee et al 1981;Lee & Crothers, 1982;Yabuki et al 1982;Roche et al 1984;Mithieux et al 1984;Marion, 1984;Chauvin et al 1985;Marion et al 1985;Marquet et al 1990). It is not clear why positive LD is not observed in electric fields for chromatin condensed with di-and multivalent cations, but one possible explanation is as follows (Kubista et al 1990 a): if chromatin orientation in electric fields is caused by polarization of DNA counter ions, as is the case for the orientation of DNA (Fredericq & Houssier, 1973;Porschke, 1985), the orientation of chromatin in the electric field will depend on its local structure.…”