Researchers have, for the first time, directly observed two DNA double helices aligning side by side in a way that supports a long-discussed idea in molecular biology. The study suggests that positively charged ions can help reduce the natural repulsion between DNA strands and guide them into a stable pairing.
A molecular "zipper" comes into view
Teams from the University of Sheffield and the University of York used high-resolution atomic force microscopy to examine DNA in liquid environments containing nickel, calcium, and magnesium ions. In the clearest images, the helices matched groove to groove, exactly as predicted by the electrostatic DNA zipper model proposed about 25 years ago.
The researchers also combined imaging with computer simulations. Their results indicate that divalent ions can sit around the DNA and act like tiny bridges, softening the charge-based push between the molecules. In some cases, a short sequence such as GTAC appeared especially effective at stabilizing the contact.
Across DNA fragments of 339 base pairs, about 10% to 14% showed pairing, usually lasting for three to four turns of the helix. The team found that perfect sequence matching was not always required for the first contact, hinting at a two-step process: ions bring molecules close, then structural compatibility helps lock them together.
While the experiments were performed on purified DNA outside living cells, the findings offer a fresh physical framework for understanding recombination, chromosome organization, and gene regulation. Published in Nucleic Acids Research, the study may help scientists map genome regions where DNA pairing plays a special role. In the future, this insight could deepen our understanding of how genetic information is organized and read with precision.
