Internal motion of deoxyribonucleic acid in chromatin. Nanosecond fluorescence studies of intercalated ethidium

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Abstract
The internal motions of DNA in a nucleosome core particle and chromatin were investigated by measuring the ns fluorescence depolarization of intercalated ethidium. Assuming that the observed anisotropy decay originates from the torsional motion of DNA, the dynamics of DNA was analyzed in a nucleosome core particle and in chromatin in detail. DNA in a nucleosome core particle has a torsional rigidity similar to that of DNA in solution and that even at the point of the ionic bonds between DNA and a histine octamer the torsional motion of DNA is not completely inhibited. The dynamics of linker DNA in chromatin were found to reflect the overall structural state of the chromatin: the motion of linker DNA was suppressed as the structure of chromatin turned from an extended state to a condensed one. In solenoidal chromatin, nucleosome movements in chromatin seem largely suppressed. The torsional rigidity of linker DNA may be increased as it is forced to bend in solenoidal chromatin.