Structure monomorphism of RNA G-quadruplex that is independent of surrounding condition.

G-quadruplex structures in nucleic acids have become attractive targets of study because their distinct structural forms may have diverse biological functions. Here, we preliminary investigated the structure and thermodynamics of G-quadruplexes of RNAs and corresponding DNAs of the same sequence by CD, UV and PAGE. Structural analysis demonstrated that the RNA sequences folded into a parallel-stranded G-quadruplex independently of surrounding conditions with different cations (K(+) and Na(+)) under both dilute and molecular crowding conditions. In contrast, G-quadruplexes of their corresponding DNA sequences showed structural polymorphism depending on the surrounding conditions. Moreover, it was demonstrated that parallel G-quadruplexes of the RNA sequences were more stable than either parallel or antiparallel G-quadruplexes of the same DNA sequences. These results allow us to propose a single, robust RNA G-quadruplex structure that exists under various conditions.