M. H. Moore

Repeat tracts of guanine bases found in DNA and RNA can form tetraplex structures in the presence of a variety of monovalent cations. Evidence suggests that guanine tetraplexes assume important functions within chromosomal telomeres, immunoglobulin switch regions, and the human immunodeficiency virus genome. The structure of a parallel-stranded tetraplex formed by the hexanucleotide d(TG4T) and stabilized by sodium cations was determined by x-ray crystallography to 1.2 angstroms resolution. Sharply resolved sodium cations were found between and within planes of hydrogen-bonded guanine quartets, and an ordered groove hydration was observed. Distinct intra- and intermolecular stacking arrangements were adopted by the guanine quartets. Thymine bases were exclusively involved in making extensive lattice contacts.

Infinite channels with a diameter 10.5 Å are formed by the DNA-base hybrid 1 in the solid state. These channels arise because 1 specifically communicates the hydrogen bonding codes of the nucleobases cytosine and guanine (“C” and “G”) to unambiguously assemble hexagonal, macrocyclic aggregates 16, which overlap in the crystal.