Structure of DNA in a nucleosome core at high salt concentration and at high temperature.

We have used hydroxyl radical cleavage of DNA to probe the organization of the nucleosome core at high salt concentration and high temperature. The rotational and translational positioning of a DNA fragment, containing part of the Xenopus borealis 5S RNA gene, on the histone octamer is maintained between salt concentrations of 0.0 and 0.8 M NaCl and between temperatures of 0 and 75 degrees C. These results provide evidence that the energy of bending DNA around the nucleosome is independent of salt concentration and temperature in this range. They illustrate the severe energetic requirements necessary to displace DNA from previously organized contacts with histones in the nucleosome core.