Influence of supercoiling on the disruption of dsDNA.

We propose that supercoiling energizes double-stranded DNA (dsDNA) so as to facilitate thermal fluctuations to an unzipped state. We support this with a model of two elastic rods coupled via forces that represent base-pair interactions. Supercoiling is shown to lead to a distention of base pairs over a short span of dsDNA. This enhances the thermal probability for their disruption. The localized region of distention is analogous to a soliton. Our theory permits the development of an analogy between the unzipping transition and a second-order phase transition, for which the possibility of a new set of critical exponents is identified.