Scientists have found that twisting structures in DNA long mistaken for knots are actually something else entirely.

Inside cells, DNA gets twisted, copied, and pulled apart. The twists can influence how genes function, affecting which are switched on and when. Studying how DNA responds to stress can help scientists better understand how genes are controlled, how the molecule is organized, and how problems with these processes might contribute to disease.

For years, researchers have been using nanopores — tiny holes just wide enough for a single DNA strand to slip through — to read DNA sequences quickly and inexpensively. These systems work by measuring the electrical current flowing through the nanopore. When a DNA molecule passes through, it disrupts that current in a distinct way that corresponds with each of the four "letters" that make up DNA's code: A, T, C and G.

Unexpected slowdowns or spikes in this signal were often interpreted as knots in DNA. But now, a new study published Aug. 12 in the journal Physics Review X finds that these signal changes can also signify plectonemes, which are natural coils that form when DNA twists under stress.