Scientists have revealed how tiny metal ions help DNA molecules overcome electrical repulsion and “zip” together with striking precision.

DNA molecules carry the same negative charge, so they would normally be expected to push apart. Inside living cells, however, DNA must sometimes come together for processes such as genetic recombination, gene silencing and cancer development.

Researchers have now observed how that pairing can happen with striking precision. Using high-powered atomic force microscopy, the team watched short DNA fragments align groove for groove. Computer simulations then showed that positively charged metal ions can settle into those grooves and act as tiny molecular bridges that help hold the two DNA molecules together.