DNA rings with multiple energy minima

Within the context of DNA rings, we analyze the relationship between intrin sic shape and the existence of multiple stable equilibria, either nicked or cyclized with the same link. A simple test, based on a perturbation expans ion of symmetry breaking within a continuum elastic rod model, provides goo d predictions of the occurrence of such multiple equilibria. The reliabilit y of these predictions is verified by direct computation of nicked and cycl ized equilibria for several thousand DNA minicircles with lengths of 200 an d 900 bp. Furthermore, our computations of equilibria for nicked rings pred ict properties of the equilibrium distribution of link, as calculated by mu ch more computationally intensive Monte Carlo simulations.