Cover: The potential energy surface for a (single strand) GC dinucleotide monophosphate fragment computed in the principal conformational subspace derived from crystal structure data on DNA duplexes. Six low energy valleys on the surface correspond to distinct conformational states of DNA, which include known and newly identified substates within the A- and B-form families. A schematic representation of the structure of each state is provided, with the guanine (5′) and cytosine (3′) bases as black and red lines, respectively (the centre of mass of each fragment is indicated as a distinctly coloured circle). The energy differences between the local energy minima within each valley are in the range 1.9–16 kcal mol−1; the energy barriers between states vary between 1 and 6 kcal mol−1. The energy surface is truncated, for clarity, at 40 kcal mol−1, relative to the global energy minimum corresponding to the BI-form. The potential energies were computed using the AMBER force field, with a distance dependent dielectric permitivity. This energy landscape is representative of a range of thermodynamic and dynamic properties of DNA, e.g. the relative trend of base-specific A- and B-form propensities and the pathway of the A- to B-form conformational transition. For further information see the article by Elsawy et al. in this issue [Nucleic Acids Res. (2005), 33, 5749–5762].
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