New Twisted 'Knot' Human DNA Structure Discovered—and It Looks Nothing Like the Double Helix

Scientists have discovered a new structure inside human cells: a never-before-seen twisted "knot" of DNA. Dubbed the "i-motif," this four-stranded knot looks totally different from the iconic double helix.

A team of researchers have homed in on these shapes in living human cells, which were previously studied only under artificial conditions in the lab. The scientists think the structure, which was detailed in a scientific paper published Monday in Nature Chemistry, might have crucial implications for the way DNA is "read."

4_23_Double Helix DNA
An artist's impression shows the famous double-helix DNA structure. Now, scientists have found a four-stranded twisted "knot" structure in human cell lines. National Human Genome Research Institute/Handout/Reuters

Our cells carry key genetic instructions for growth and functioning in the form of DNA. Coded into letters—A, C, G and T—these instructions govern the way our bodies look and the way they work.

In 1953, James Watson and Francis Crick discovered the now-famous "double helix" DNA structure. But scientists have previously observed short lengths of DNA in different shapes. "When most of us think of DNA, we think of the double helix," Daniel Christ, an associate professor at the Garvan Institute of Medical Research in Australia, who co-led the research, said in a statement. "This new research reminds us that totally different DNA structures exist—and could well be important for our cells."

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These shapes, researchers think, could affect the way genetic instructions are recognized within the body. "In the knot structure, C letters on the same strand of DNA bind to each other," said research co-lead Marcel Dinger in the statement. "This is very different from a double helix, where 'letters' on opposite strands recognize each other, and where Cs bind to Gs [guanines]." Like Christ, Dinger is an associate professor at the Garvan Institute.

The researchers used a fine-tuned antibody tool to track down the strange structures and confirm their existence in living cells. They took a tiny fragment of an antibody molecule that found and fastened itself to i-motif structures. Importantly, the molecular sliver didn't recognize double-helix-shaped DNA or a similar four-stranded "G-quadruplex" shape.

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The team tracked the i-motif structures using fluorescence, which highlighted the i-motif DNA structures as green dots.

"What excited us most is that we could see the green spots—the i-motifs—appearing and disappearing over time, so we know that they are forming, dissolving and forming again," explained Mahdi Zeraati, another study author, who is also with the Garvan Institute. This coming and going, he added, hints at the function of the structures. "It seems likely that they are there to help switch genes on or off, and to affect whether a gene is actively read or not," Zeraati said.

The fleeting nature of these weird little knots may also explain why it's been so hard to nail them down, Christ added.

"These findings will set the stage for a whole new push to understand what this new DNA shape is really for, and whether it will impact on health and disease," Dinger said.