Meet the More Durable XNA

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Synthetic molecules resembling DNA can function and evolve just like the real thing, its developers say.

These new, unnatural building blocks could be more useful than DNA or its closely related biomolecule, RNA, in a variety of medical and biotechnology applications, researchers added. Other investigators noted they could even lead to novel forms of life.

DNA is essentially made of four different kinds of molecules known as nucleic acids, commonly referred to by their initials, A, G, C and T. These run along a backbone made of sugars and phosphate groups.

Scientists call their artificial nucleic-acidlike molecules XNA, in which the natural sugar component has been replaced by one of six alternative organic compounds. These XNA molecules all can bind to DNA and RNA.

The researchers also have developed enzymes that can synthesize XNA from a DNA template, plus others that can "reverse transcribe" XNA back into DNA. This means they can store and copy data just as DNA can ? the basis of heredity for all life on Earth.

The investigators subjected an XNA molecule to artificial natural selection in the lab by introducing mutations into its genetic code. By allowing the different versions of the molecule to compete against each other for binding to another molecule, the team ended up with a shape that bound tightly and specifically to the target ? just as one would expect of DNA under the same conditions. This makes XNA the only known molecules other than DNA and RNA capable of Darwinian evolution.

"Heredity ? information storage and propagation ? and evolution, two of the hallmarks of life, can be implemented in polymers other than DNA and RNA," researcher Philipp Holliger at the Medical Research Council Laboratory of Molecular Biology in Cambridge, England.

One notable property of XNA molecules is they are not biodegradable: They are impervious to natural enzymes that degrade DNA and RNA. As such, they could find use in medical and biotechnology arenas where DNA and RNA could not go.

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