For seventy years, molecular biologists have relied on restriction enzymes to cut DNA into pieces that can be stitched back together, gene by gene. These proteins are picky: each recognizes only a short sequence, and when it cuts, it leaves a “sticky end” of just four unpaired bases, a short overhang the two fragments use to bond. Four bases isn’t much to hold onto, and when assembling long, complex DNA, say for a gene therapy vector or an mRNA cancer vaccine library, that “short handshake” becomes a bottleneck.
A team at Nagoya University, led by Hiroshi Abe and Masahito Inagaki, may have found a way around the problem, without enzymes. Published in Nucleic Acids Research, their method tags the DNA backbone at the cut site with a sulfur atom, then exploits the strong natural affinity between silver and sulfur. Silver nanoparticles bind that tag and act as a Lewis acid, triggering a reaction that severs the strand exactly there, no sequence recognition, no enzyme required. The cut fragment sticks to the nanoparticle while the desired piece stays free in solution, so a brief spin in a centrifuge separates them.
The catch was that bare silver nanoparticles tend to clump together in solution, and once they do, much of their reactive surface, the part that grabs the sulfur tag and triggers the cut, gets buried inside the clump and stops working. That is why the initial approach recovered only 14% of the desired DNA. The fix borrowed a trick from nanomedicine: coating each nanoparticle in polyethylene glycol (PEG), a water-soluble polymer that acts like a non-stick layer, keeping the particles separated so their full surface stays available to react. Cleavage efficiency at body temperature then jumped from 36% to 92%, and DNA recovery rose to a striking 98%. The method also generates overhangs of 8 to 18 bases instead of 4, and with the longest ones, joining efficiency reached 44%, roughly five times better than conventional enzymes. As proof of concept, the team assembled an 848-base-pair DNA construct and used it to make living cells produce a fluorescent protein, confirming the DNA was fully functional.
The technique is still limited to joining two fragments at a time, and genome-scale assembly is still ahead. It also depends on custom-synthesized, modified DNA rather than off-the-shelf enzymes, which could raise costs for smaller labs. Still, by trading sequence recognition for chemistry, this approach frees genetic engineers from one of the field’s oldest constraints, and could speed how next-generation therapies move from concept to clinic.
PR
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