Synthetic DNA replicated by living organism for first time in U.S. study

Scientists have taken the first steps toward rewriting the blueprint of life using laboratory-made DNA base pairs not seen in nature.

Findings open the door for a host of new organisms that coud produce medical drugs

Scientists have created the first living organism to replicate itself using an expanded genetic code that includes two entirely synthetic DNA bases, creating the potential for new life forms that produce pre-programmed biological molecules. (Shutterstock)

Scientists have taken the first steps toward writing the blueprint of life in an alphabet unknown to nature, they reported online in the journal Nature this week.

Until now, biologists synthesizing DNA in the lab have used the same molecules — called bases — that are found in nature. But Floyd Romesberg of the Scripps Research Institute in La Jolla, Calif., and colleagues not only created two new bases, but also inserted them into a single-cell organism and found that the invented bases replicate like natural DNA, though more slowly and only if the building blocks are supplied. 

The scientists reported that they got the organisms, the common bacteria E. coli, to replicate about 24 times over the course of 15 hours.

Four nucleotide bases, denoted as A,T,G and C, form two base-pairs that combine to create genes. Genes in turn code for proteins. Researchers have inserted an entirely new, synthetic base-pair into bacterial DNA. The bacterium was then able to replicate the synthetic base-pairs, as long as the molecular building blocks were supplied by researchers. (Nature)

The accomplishment "redefines this fundamental feature of life," wrote biologists Ross Thyer and Jared Ellefson of the University of Texas, Austin, in a commentary in Nature on Wednesday.

The booming field of synthetic biology holds promises for creating new antibiotics and other drugs. It has also raised concerns scientists are "playing God" by creating living things that could escape from labs into the outside world with nothing to check their spread.

In the current experiment, the scientists took pains to make that impossible, according to their paper. The new bases are not found in the natural environment, Romesberg and his colleagues said, so even if organisms with man-made DNA were to escape from the lab they could not survive, let alone infect other organisms.

X and Y, meet A, T, C and G

In nature, DNA base molecules, designated A, T, C, and G, pair up. A pairs with T and C with G, forming what looks like steps in a winding staircase — the double helix that is the DNA molecule. Bases determine what amino acids a particular strand of DNA codes for, and therefore what proteins (long strings of amino acids) are produced.

So far, the synthetic bases, which Romesberg's team call X and Y, do not code for any amino acids, the scientists reported. But in principle they — or other synthetic bases — could.

Much as adding a 27th and 28th letter to the English alphabet would allow more words to be created, so adding X and Y to the natural DNA bases would allow new amino acids and proteins to be created. Unknown at this early stage is whether the new proteins would be functional or effectively useless.

Believing that they will be useful, Romesberg co-founded a biotechnology company named Synthorx, which was officially launched on Wednesday. Based in San Diego, Calif., it will focus on using synthetic biology "to improve the discovery and development of new medicines, diagnostics and vaccines," the company said in a statement.

Synthorx has the exclusive rights to the synthetic DNA advance.


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