The Ring-Shaped Protein That Catches DNA and Pulls It Together
Every cell in your body carries about two metres of DNA, folded and packed into a nucleus far too small to hold it stretched out. Something has to organise that enormous tangle, keep it from breaking, and help repair it when it does. Scientists have now filmed one of the organisers at work — and it changes shape as it does its job.
Researchers at Kanazawa University and the National Institute of Genetics in Japan used high-speed atomic force microscopy to watch a protein assembly called Smc5/6 as it interacted with DNA. Their study is published in Nature Communications. Unlike ordinary microscope pictures, which show a single frozen moment, this technique records a film: a very fine probe follows movements and changes at the nanometre scale, billionths of a metre across.
Two shapes: I and O
Smc5/6 is made of several proteins working together. It belongs to a family of protein assemblies that maintain chromosomes, the structures that carry DNA inside cells. Scientists already knew it mattered for DNA maintenance and repair, but exactly how it captured and handled DNA had been hard to see.
The team studied purified Smc5/6 from budding yeast — the same kind of yeast used in baking and brewing — under controlled laboratory conditions. They found the assembly could take two distinct shapes. In one, its two long arms lay close together, looking like the letter I. In the other, the arms separated into an open ring, like the letter O.
The switch between the two shapes was influenced by ATP, the molecule cells use to supply energy. Binding ATP encouraged the open shape, and later ATP-related changes were linked to different ways of holding DNA.
Catching, tethering and packing
The films showed Smc5/6 meeting DNA in more than one way. Sometimes DNA was held near one end of the assembly. Sometimes it sat inside the ring formed by the arms — direct evidence of how the assembly can capture DNA.
The researchers also saw Smc5/6 touching two separate sections of DNA at the same time and holding them together, a process called tethering. And when it interacted with twisted DNA, the DNA took up less space than DNA on its own. Together, these observations suggest Smc5/6 helps pack DNA more tightly by bringing sections together and steadying twisted arrangements.
Kenichi Umeda of Kanazawa University, the study's first author, said: "By observing individual Smc5/6 structures as they interacted with DNA, we could see how changes in their shape are associated with different ways of capturing and holding DNA. These observations bring us closer to understanding how this protein assembly carries out its roles in maintaining chromosomes."
What this does — and does not — show
This is fundamental biology, not a medical treatment. The experiments used purified proteins and DNA outside living cells, so they reveal how the molecules behave under controlled conditions rather than proving every step inside a living cell. The authors are careful about that limit, and so should we be.
Even so, the result matters. DNA maintenance and repair go wrong in many diseases, and understanding the physical machinery — how a protein opens, catches, holds and packs its cargo — is the first step towards understanding what happens when that machinery fails. Sometimes the biggest ideas in biology are also the smallest: a ring a few billionths of a metre wide, opening and closing, keeping the instructions for life in order.
If your child is curious about how the tiny machinery inside cells actually works, a first lesson in biology or chemistry can start with DNA packing and end with why shape matters as much as chemistry. Book your first lesson
Sources:
- Umeda, K., Kurokawa, Y., Kodera, N. and Murayama, Y., "Submolecular video-imaging of the Smc5/6 complex topologically bound to DNA", Nature Communications 17, 10398 (2026), DOI: 10.1038/s41467-026-77122-x, as reported 4 November 2026: https://www.prnewswire.co.uk/news-releases/kanazawa-university-research-scientists-discover-how-a-ring-shaped-protein-captures-and-brings-together-dna-strands-302928901.html
London Tutors — post your tutoring request and we will match you with a verified tutor.