DIFFERENTIAL BEHAVIOR OF CURVED DNA UPON UNTWISTING

We have synthesized DNA segments with different handedness, twisting a nd radii of curvature, and have analyzed the effect of untwisting on t hem. The results indicate that the dynamic behavior of curved DNA upon untwisting is strongly determined by the initial sequence-dependent D NA trajectory. In particular, DNA with the same radii but with opposit e handedness of superhelix twisting can show very different conformati onal responses to ethidium bromide untwisting. Upon treatment with eth idium bromide, right-handed superhelixes decrease their twist and incr ease the planarity of the superhelix, while left-handed superhelixes i ncrease twisting and decrease their degree of planarity.