TOPOLOGICAL INTERACTIONS IN MULTIPLY LINKED DNA RINGS

The elasticity of DNA catenanes, i.e., multiply linked DNA rings, is i nvestigated using the Gauss invariant as a minimal model for topology conservation. An effective elastic free energy as a function of the di stance R between segments located on different rings is obtained. An a nharmonic part at large distances, growing as R-4, if R >> R-G (R-G be ing the radius of gyration), is found, for R << R-G the interaction is strongly repulsive. Calculated distribution functions for the distanc e between segments located on different rings for several linking numb ers are in qualitative agreement with distribution functions obtained experimentally from electron micrographs of DNA catenanes [S. D. Leven e et al., Biophys. J. 69, 277 (1995)].