If any proof were needed of DNA's versatile roles and use, it is certainly provided by the numerous depositions of new three-dimensional (3D) structures to the coordinate databanks (PDB, NDB) over the last two years. Quadruplex motifs involving G-repeats, adducted sequences and oligo-2'-deoxynucleotides (ODNs) with bound ligands are particularly well represented. In addition, structures of chemically modified DNAs (CNAs) and artificial analogs are yielding insight into stability, pairing properties, and dynamics, including those of the native nucleic acids. Besides being of significance for establishing diagnostic tools and in the analysis of protein-DNA interactions, chemical modification in conjunction with investigations of the structural consequences may yield novel nucleic acid-based therapeutics. DNA's predictable and highly specific pairing behavior makes it the material of choice for constructing 3D-nanostructures of defined architecture. Recently the first examples of DNA nanoparticle and self-assembled 3D-crystals were reported. Although the structures discussed in this review are all based either on X-ray crystallography or solution NMR, small angle X-ray scattering (SAXS), and cryoEM are proving to be useful approaches for the characterization of nanoscale DNA architecture.
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