Evidence for the tetraplex structure of the d(GT)n repetitive sequences in solution

Abstract

The ability of oligonucleotides 3′-d(GT)₅pO(CH₂)₆Opd(GT)₅-5′(anti[d(GT)]) and 3′-d(GT)₅pO(CH₂)₆Opd(GT)₅-3′(par[d(GT)]) to form tertiary structures has been studied. Circular dichroism (CD) as well as the fluorescence of the ethidium bromide (E1Br) complexes with oligonucleotides and hydrodynamic volume measurements in solutions containing 0.01 M phosphate buffer, pH 7 and NACl in concentrations from 0.1 M to 1 M, have been used. The data obtained in the temperature interval from 30°C to 10°C are in good agreement with the structure suggested earlier [1] where the par[d(GT)] and anti[d(GT)] form structures with four parallel strands in which layers of four G-residues alternate with unpaired bulged-out T-residues. Ethidium bromide interacts with the structure in a cooperative manner. Two ethidium bromide molecules intercalate between two layers of four G-residues.