In a world first, scientists in Australia have identified a new form of DNA inside human cells. Given the name i-motif, the DNA resembles a twisted knot rather than the double helix shape we all know so well.
The discovery was made by researchers from the Garvan Institute of Medical Research in Sydney and is reported in Nature Chemistry.
DNA is composed of four chemical bases: adenine (A), guanine (G), cytosine (C) and thymine (T). The double-helix structure – discovered in 1953 by James Watson and Francis Crick – is formed by A binding with T, and C binding with G. However, even in this stable double-helix shape, the DNA molecule is constantly changing. For example, when a piece of DNA is being replicated the two strands are pulled apart and paired with new sequences. DNA molecules also separate when the instructions for a gene are being read by the cell. When the process is over, the strands zip back together.
In the i-motif structure, C bases on the same strand of DNA bind to each other. Consequently, there needs to be a cytosine-rich area for the piece of DNA to fold itself into the i-motif shape. It also only occurs in a relatively small region of a genome and sticks out like a bumpy knot.
“Our imaging suggests that this is a normal thing that happens”, said Marcel Dinger, a molecular biologist who oversaw the research. “It is very likely that genomes in all the cells of our bodies are forming i-motifs at some point in time.”
It was way back in the early 1990s when French scientists discovered that a region of a DNA strand could fold on top of itself, creating a four-stranded shape in which C bases paired up. Indeed, scientists have long known that DNA can fold into other forms in the laboratory including crosses and U shapes.
The question is, does DNA and its flexibility for taking on new shapes have any biological relevance? We wait to hear much more about this research area soon.