Like charges normally repel one another, yet DNA molecules must pair up inside living cells to carry out essential biological processes. That pairing plays a crucial role in genetic recombination, gene silencing, and the development of cancer, and until now, exactly how two negatively charged DNA strands manage to overcome their mutual repulsion and lock together had remained a long-hypothesized but unseen mechanism.
Using high-powered atomic force microscopy, researchers at the University of York observed short DNA fragments matching up with exact precision, groove for groove. Advanced computer simulations then revealed the mechanism behind what the microscopy showed: positively charged metal ions act as tiny molecular bridges, nestling inside the grooves of the DNA to lock the two strands together.
Watching a Long-Hypothesized Mechanism Unfold
“It was incredible to be able to directly visualise the long-hypothesised mechanism for the first time,” said Dr Thomas Catley of the University of Sheffield, one of the study’s authors. Dr Victor Velasco-Berrelleza, also of Sheffield, added that combining the two techniques was key to understanding not just what happens, but why: “Microscopy shows us what happens, but the simulations allows us to uncover the molecular mechanism behind it.”
Professor Agnes Noy of the University of York, who led the research, said the discovery opens a path toward understanding where in the genome this kind of DNA-DNA pairing matters most. “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,” Noy said.
Why the Mechanism Matters
DNA-DNA pairing of this kind underlies processes as fundamental as how cells repair damaged genetic material and how genes are switched on or off. Understanding the physical, ion-mediated mechanism that allows two strands to find and bind to each other gives researchers a new lens for studying what happens when that process goes wrong — including in cancer, where disrupted genome regulation is a hallmark of disease.
By pairing direct visualization with molecular simulation, the team was able to move past indirect inference and actually watch the process unfold at atomic resolution — a combination the researchers say offers a template for probing other elusive molecular mechanisms inside the cell.
The study, “Imaging and mechanism of DNA–DNA recognition mediated by divalent ions,” was published in Nucleic Acids Research (DOI: 10.1093/nar/gkag817).