What bridges the gap between two repellent molecules?

The simulations pointed to double-charged metal ions, known as divalent ions. Each of these ions can effectively behave like two charged arms. One arm interacts with one DNA molecule while the other grips the second, forming a bridge across the space that separates the two strands and holding them in alignment.

This mechanism finally provides experimental support for the "DNA zipper" model, an idea proposed about twenty years ago by Professor Alexey Kornyshev from Imperial College London and his collaborators. Their theory held that salt ions surrounding DNA could produce alternating patterns of electrical charge, which would help neighboring DNA molecules align with one another. Until now, directly observing this proposed mechanism had proved difficult.

Professor Agnes Noy, from the School of Physics, Engineering and Technology at the University of York, co-led the research. She said: "This discovery could help researchers identify regions of the genome specially involved in DNA pairing. These regions may become particularly important when mutations disrupt normal cellular processes and contribute to cancer."

Do all DNA sequences pair equally well?

No — and that is one of the study's most practically useful findings. DNA does not pair equally well along every sequence. Some stretches of DNA created much stronger contacts than others, producing distinct hotspots where two helices were especially likely to line up.

That finding could help researchers pinpoint parts of the genome that are particularly involved in DNA recognition and pairing. Such regions may become especially significant when mutations interfere with normal cellular activity and contribute to cancer.

Dr. Thomas Catley, co-lead author from the School of Chemical Materials and Biological Engineering at the University of Sheffield, said: "It was incredible to be able to directly visualize the long-hypothesized mechanism for the first time. The advanced imaging techniques at our disposal are allowing us to uncover these key DNA interactions which have implications in many key cellular processes."

What could this mean for medicine and biotechnology?

The discovery has potential uses beyond medicine. Because some DNA sequences can be programmed to interact more strongly than others, scientists may eventually be able to exploit these properties to build customized DNA structures for biotechnology applications.

A few caveats are worth keeping in mind. The researchers observed short pieces of DNA under controlled laboratory conditions, not full genomes inside living cells. The hotspot findings also come from a specific set of sequences, so researchers will need further work to map pairing behavior across the genome and confirm how the mechanism operates in natural cellular contexts.

Still, the study marks a milestone: a two-decade-old hypothesis about how DNA overcomes electrical repulsion now has direct visual and computational evidence behind it. The paper, "Imaging and mechanism of DNA-DNA recognition mediated by divalent ions," appears in Nucleic Acids Research, volume 54, issue 16 (DOI: 10.1093/nar/gkag817), authored by Thomas E. Catley, Victor Velasco-Berrelleza, Daniel E. Rollins, Alice L. B. Pyne and Agnes Noy.