Quadruplex structures in nucleic acids

DNA oligonucleotides that have repetitive tracts of guanine bases can form G-quadruplex: structures that display an amazing polymorphism. Structures o f several new G-quadruplexes have been solved recently that greatly expand the known structural motifs observed in nucleic acid quadruplexes. Base tri ads, base hexads, and quartets that contain cytosine have recently been ide ntified stacked over the familiar G-quartets. The current status of the div erse array of structural features in quadruplexes is described and used to provide insight into the polymorphism and folding pathways. This review als o summarizes recent progress in the techniques used to probe the structures of G-quadruplexes and discusses the role of ion binding in quadruplex-form ation. Several of the quadruplex structures featured in this review can be accessed in the online version of this review as CHIME representations. (C) 2001 John Wiley & Sons, Inc.