CRYSTALLOGRAPHIC STUDIES OF DNA HELIX STRUCTURE

X-ray crystallography can reveal the three-dimensional structure of sh ort fragments of DNA or RNA with unique precision. It provides informa tion concerning both the global helical structure and the geometry of local features such as base-pair stacking patterns and backbone confor mation. An analysis of the structures of a family of DNA decamers with related sequences, crystallizing in a number of different lattices, d efines the ranges in which conformational parameters can vary in B-DNA helices and shows the correlations between them. Thus, these studies show the static structures and give insight into the mechanics of DNA helices by showing how a change of one local conformational parameter will influence others. Crystal structures are also used to assess the competing influences of nucleotide sequence and environment on the thr ee-dimensional DNA structure. To extrapolate from DNA crystal structur es to physical characteristics and function of these molecules in solu tion or embedded into a defined sequence context remains a major chall enge.