10] Guanine quartet structures

Abstract

Publisher Summary Of the five nucleosides commonly found in DNA and RNA, only guanosine is capable of forming extensive self-structures in solution, hydrogen bonding with itself to give G–G base pairs, and guanine quartets. The formation of these structures was found to be uniquely dependent on monovalent cations and on the identity of the cation. Recently, natural sequences from chromosomal telomeres and immunoglobulin switch regions were shown to form two different kinds of noncanonical structures: parallel quadruplexes containing G quartets and fold-back duplexes containing G–G base pairs. Further investigation has shown that quartet structures constitute a closely related family, whose individual members differ in their overall molecularity and in the relative orientations of their strands. The formation of these alternative structures by specific sequences depends on such factors as temperature, DNA concentration, and on the molar ratios of sodium and potassium ions in the reaction buffers. G4-DNA is formed by single-stranded DNA molecules that contain either simple or complex guanine motifs, which means short single stretches of 3–10 contiguous guanines in a DNA molecule or multiple stretches of contiguous guanines separated from each other by other bases, respectively.