For billions of years, life has danced that same old DNA jig. At some
point after Earth’s formation, but before bacterial slime formed the
planet’s oldest fossils 3.7 billion years ago, DNA became the system by
which virtually every organism stored and passed on its genetic
information. No matter how many times mutations or natural selection
remixed the tune, four nitrogenous base units always comprised DNA:
adenine, cytosine, guanine and thymine. This was as true for hairy apes
as it was for brewer’s yeast, redwoods and Tyrannosaurus rex.
Now, scientists led by the Scripps Research Institute in La Jolla,
California, have added two extra, artificial letters to the ancient
alphabet of A, C, G and T. And the E. coli living with this unusual
six-letter, three-base-pair alphabet are, by the account published
Monday in the Proceedings of the National Academy of the Sciences,
capable of surviving tough laboratory conditions. Read more
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