Helix Geometry and Hydration in A-DNA, B-DNA, and Z-DNA

Abstract

The development of practical methods of large-scale, high-purity DNA oligonucleotide synthesis (Tan et al., this volume) has made it possible for the first time to carry out single-crystal X-ray structure analyses of short DNA molecules of preselected sequence. This has revolutionized our knowledge of the detailed molecular structure of DNA in much the same way that the perfection of multiple isomorphous replacement phase analysis did for proteins in the early 1960s. As listed in Table 1, at least three independent structure analyses are now available for each of the two families of DNA double helix known from fiber studies—A and B—plus a new and previously unsuspected family, left-handed Z-DNA. These analyses, of helices whose crystallographically unique units range from 3 bp to 12 bp, represent an advance beyond earlier studies of monomers and dimers (for review, see Rich et al. 1979), since they offer better approximations of the geometry that...