All guanine-rich DNA and RNA molecules tend to fold into inter- and intra-molecular structures called G-quadruplexes.
The core of a G-quadruplex is composed of at least two adjacent G-tetrads stabilized by monovalent cations.
While it has been suggested that there could potentially be over 375 000 quadruplex forming sequences
in the human genome alone, only a small number of three-dimensional G-quadruplex structures are known. More
structural data are needed to explain their presence and function in vivo. We offer here a short review of experimental
methods commonly used to determine G-quadruplex topologies.