Polymorphism of DNA versus Structural Conservatism of RNA: Classification of A-, B-, and Z-TYPe Double Helices

Abstract

In Chapters 10 to 15, the molecular structures of oligo- and polynucleotides are discussed together because they are intimately related. In most of the known oligonucleotide crystal structures, self-complementary, double-helical arrangements are observed. While limited in length between 2 and 12 base-pairs, these reveal fine details of polynucleotide self-assembly, hydration, and metal ion coordination. In addition, oligonucleotides sometimes crystallize as nonhelical entities with extended or looped configurations; this indicates how flexible the nucleotide building block or the phosphodiester swivel link between the individual nucleotides may be. As described in Chapter 15, the crystal structure of tRNA offers a wealth of structural information both on double-helical and on nonhelical polynucleotide domains.