'Quadruple helix' DNA seen in human cells

Cambridge University scientists say they have seen four-stranded DNA at work in human cells for the first time.

The famous "molecule of life", which carries our genetic code, is more familiar to us as a double helix.

But researchers tell the journal Nature Chemistry that the "quadruple helix" is also present in our cells, and in ways that might possibly relate to cancer.

They suggest that control of the structures could provide novel ways to fight the disease.

"The existence of these structures may be loaded when the cell has a certain genotype or a certain dysfunctional state," said Prof Shankar Balasubramanian from Cambridge's department of chemistry.

"We need to prove that; but if that is the case, targeting them with synthetic molecules could be an interesting way of selectively targeting those cells that have this dysfunction," he told BBC News.

The team, led by Giulia Biffi, a researcher in Balasubramaninan's lab, produced antibody proteins that were designed specifically to track down and bind to regions of human DNA that were rich in the quadruplex structure. The antibodies were tagged with a fluorescence marker so that the time and place of the structures' emergence in the cell cycle could be noted and imaged.

This revealed the four-stranded DNA arose most frequently during the so-called "s-phase" when a cell copies its DNA just prior to dividing.