Crystal and molecular structure of a DNA duplex containing the carcinogenic lesion O6-methylguanine

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Abstract
The crystal and molecular structure of the first DNA duplex containing the carcinogenic lesion O6MeG has been determined to a resolution of 1.9 .ANG. and refined to an R factor of 19%. {d[CGC-(O6Me)GCG]}2 crystallizes in the left-handed Z DNA form and has crystal parameters and conformational features similar to those of the parent sequence [d(CG)3]2. The methyl groups on O6 of G4 and G10 have C5-C6-O6-O6Me torsion angles of 73.degree. and 56.degree., respectively, and protrude onto the major groove surface. The base-pairing conformation for the methylated G .cntdot. C base pairs is of the Watson-Crick type as opposed to a wobble-type conformation that had been proposed in a B DNA fragment. As in other Z DNA structures, a spine of hydration is seen in the minor groove.