Effect of gamma-irradiation on the conformation of the native DNA molecule

Extensive investigation of gamma-irradiated DNA solutions with the application of several informative physical methods suggested that at doses of 10-30 Gy the observed change in the size of the DNA molecule is due to a decrease in long-range interactions in the macromolecule. The comparison of the results of investigations of non-irradiated and irradiated DNA and its complexes with low molecular weight ligands over a wide range of ionic strengths showed that these interactions are electrostatic in nature and are due to a decrease in the charge density on the DNA molecule when its solutions are irradiated. In the irradiation dose range discussed here, the persistent length of the DNA molecule determined by short-range interactions in the chain does not undergo pronounced changes. It is shown that the free ligand in the irradiated solution can protect the DNA molecule against radiation damage. In contrast, the ligand bonded by intercalation does not exhibit this ability.