Example of the structure of a tetramolecular quadruplex

Example of the structure of a tetramolecular quadruplex (Protein Data Bank ID: 139D). This quadruplex DNA is comprised of four strands, 7 nucleotides long. Its structure was obtained by NMR (nuclear magnetic resonance spectroscopy). The sequence here mimics the Tetrahymena telomeric sequence (a ciliate protozoan). Quadruplexes are non-usual DNA structures that offer an additional level of gene regulation. In contrast to the permanent double helix structure of DNA, the very dynamic structures of quadruplexes comprise four strands rotating around each other. G4s may form in no less than 716,000 locations in our genome. They may be involved in a number of biological processes that are indispensable to the correct operation of the cell, such as chromosome stability or DNA replication. This might explain their role in the development of several rare neurodegenerative or infectious diseases.