A model of the hydrodynamic behavior of irradiated DNA: Dependence on molecular conformation

The model presented here describes the DNA viscosity and viscoelastometric responses to ionizing radiation‐induced molecular breakdown. Four DNA conformations are considered: (1) linear chain, (2) relaxed circle, (3) supercoiled circle, and (4) supercoiled linear. The model includes the systems of differential equations for calculating the size distributions of DNA molecules as functions of dose. Thedistributions are used in the usual hydrodynamic formulae for heterogeneouspopulations of polymer molecules. The sensitivity of viscoelastometry for the estimation of D₃₇ is better than that of viscometry. The model predicts a considerable difference between the radiation responsesof linear and circular DNAs. The prediction is confirmed by experimental data for T4 DNA [C. S. Lange et al. (1984) Rad. Res. 100, 1–15] and E. coli DNA [S. E. Bresler et al. (1984) Biophys. J. 45, 749–754]. Thus, ionizing radiation can be used to determine the original conformation of DNA molecules.