There is no more iconic image in biology than that of DNA's double-stranded helix, which coils and supercoils on itself to form dense chromosomes.
But a quite different, square-shaped type of DNA structure can easily be created in the laboratory by the folding of synthetic DNA strands rich in guanine, one of the building blocks of DNA. Scientists have long believed that these so-called 'G-quadruplex structures' may occasionally form in the DNA of living cells. A G-quadruplex comprises four guanines from different places along a G-rich strand held together by a special type of hydrogen bonding to form a compact square structure that interrupts the DNA helix.
In a paper published online today in Nature Chemistry1, researchers led by Shankar Balasubramanian at the University of Cambridge, UK, provide strong evidence that G-quadruplexes do occur in cells — and that these unusual structures may have important biological functions.
Protecting the chromosome
The protective tips of chromosomal DNA, known as telomeres, are rich in guanine and so are likely candidates for G-quadruplex structures. In fact, studies in cancer cells have shown that small molecules that bind and stabilize G-quadruplex structures cause DNA damage at telomeres, supporting the argument.