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 Until now, biologists who synthesize 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, California, 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.
The scientists reported that they got the organisms, the common
bacteria E. coli, to replicate about 24 times over the course of 15
hours.
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 in some way "playing God" by creating living things
that could escape from labs into the outside world where they have
no natural predators and 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 manmade DNA were to escape from the lab they could
not survive, let alone infect other organisms.
In nature, DNA's bases, 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.
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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 manmade 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 gibberish or meaningful.
Believing that they will be useful, Romesberg co-founded a
biotechnology company named Synthorx, which was officially launched
on Wednesday. Based in San Diego, California, 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.
(Reporting by Sharon Begley; editing by Andrew Hay)
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