Bending and twisting dynamics of short linear DNAs. Analysis of the triplet anisotropy decay of a 209 base pair fragment by Brownian simulation

Brownian dynamics is used to simulate the decay anisotropy of short linear DNA fragments modeled as a string of beads. The model is sufficiently general to allow for static bends, anisotropic bending, and elastic constants for bending and twisting which can vary along the chain. In limiting cases, simulations are found to be in excellent agreement with analytic theory down to a correlation length of at least 500 Å. This model is then used to analyze the 0-2.5 μs triplet depletion anisotropy decay of a 209 base pair sea urchin DNA fragment. It is concluded that the conventional worm-like chain model, in which bending is isotropic and/or there are no static bends along the chain, is unable to account for the experimental results unless a correlation length of 1000 Å is assumed. A worm-like chain with anisotropic bending requires a similar but slightly larger correlation length.