Analytical potential of the quadruplex DNA-based FRET probes

DNA exhibits structural flexibility and may adopt also tetraplex structures known as guanine-quadruplexes or G-quadruplexes. These G-quadruplexes have recently received great attention because G-rich sequences are often found in genome and because of their potential links to mechanisms that relate to cancer, HIV, and other diseases. The unique structure of quadruplexes has also stimulated development of new analytical and bioanalytical assays based on fluorescence resonance energy transfer (FRET). Intramolecular folding of a flexible single-stranded DNA molecule into a compact G-quadruplex is a structural transition leading to closer proximity of its 5'- and 3'-ends. Thus, labeling both ends of a DNA strand with donor and acceptor fluorophores enables monitoring the quadruplex formation process by means of the FRET signal. This review shows how FRET technique contributes to G-quadruplex research and focuses mainly on analytical applications of FRET-labeled quadruplexes. Applications include studies of structural transitions of quadruplexes, FRET-based selection of ligands that bind to quadruplexes, design of molecular probes for protein recognition and development of sensors for detection of potassium ions in aqueous solution.