G-quadruplex DNA
G-quadruplexes are secondary DNA structures formed by square planar arrangement of guanines residues which are hydrogen-bonded through their Watson-Crick and Hoogsteen edge. The basic unit of G-quadruplexes is G-tetrads which arise from the folding of DNA strands that comprises the stretches of tandem guanines bases. These secondary structures play important role in the regulation of various cellular processes such as DNA replication, transcription etc. G-quadruplex forming sequences are widely distributed in genome such as in telomeric region, promoter regions of oncogenes, immunoglobulin switch regions, introns, exons and UTRs of genes. Owing to the presence of these structures in the regions which are vital for proliferation of cancer cells, the G-quadruplex structures are considered as potential therapeutic targets in cancer biology.