Crystal structures of fragments of DNA and RNA

Abstract

Crystallographic analyses of oligonucleotides give the degree of detailed information about nucleic acid structure that is not obtainable from fibrous polynucleotides, which yield average structures, and globular nucleic acids such as tRNA which yield relatively low resolution data. Indeed, not until 1976 was the Watson-Crick geometry of an A-U base pair actually observed at atomic resolution, in the crystal structure of ApU (Seeman et al., 1976). The smallest unit of a polynucleotide which contains all the conformational information necessary to describe the relationship among the base, sugar and phosphodiester linkage is the dinucleoside phosphate. Since it was first demonstrated that it is possible to obtain good crystals of these molecules (Seeman et al., 1971), considerable effort has been expended in studying oligonucleotides alone and complexed with other molecules. This chapter concentrates on the uncomplexed oligonucleotides and summarises what is now known about their conformations, hydrogen bonding properties, stacking patterns and metal binding sites.