This research also shows that the number of G-quadruplex structures present in human cells can be increased by a small molecule called pyridostatin, which can stabilise G-quadruplexes in the test tube. This observation suggests G-quadruplexes are important for cellular replication. The highest number of G-quadruplexes was observed in the S phase of the cell cycle – the point at which DNA is separated into two single strands and copied prior to cell division. These antibodies were labelled with a fluorescent molecule that can be observed in a microscope, and used this to track the formation and location of G-quadruplex structures during the cell cycle. To achieve this, the researchers produced antibodies that specifically recognise G-quadruplexes but no other DNA structures. On January 20, a team of researchers at the University of Cambridge, led by Shankar Balasubramian, published a paper in Nature Chemistry showing strong evidence for the existence of G-quadruplexes in human cells and their involvement in the replication of cells. Their locations in the genome suggest they are more than a mere structural curiosity and fulfil important functions in the cell cycle. The human genome contains approximately 376,000 sequences with the potential to form G-quadruplexes. Julian Huppert/Wikimedia Commons G-quadruplexes in humans The fact that human DNA contains many guanine-rich sequences, and that these form G-quadruplexes in a test tube, was considered to be indirect evidence for their existence in human cells. This discovery was made less than ten years after the publication of the double helix structure but, until very recently, the existence of G-quadruplexes in human cells had not been proven. Stacks of these guanine quartets form a quadruple helix, also known as a G-quadruplex. Instead of pairs, sequences rich in guanine can form quartets consisting exclusively of this base. Only the number and order of the bases determines the difference between single-celled bacteria and human life.Īlthough the double helix is the most common and best known structure of DNA, this fascinating molecule is capable of adopting many other structures, including a four-stranded helix. All that’s needed is just four “bases”, arranged into pairs – adenine and thymine, cytosine and guanine – and connected to two backbones which are wound tightly around each other. The simplicity of DNA’s components and the spectacular complexity of the resulting organisms never cease to inspire a sense of wonder.
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