The discovery of the Rosetta Stone resolved a longstanding puzzle, permitting the translation of Egyptian
hieroglyphs1（象形文字） into Ancient Greek. John Chaput, a researcher at Arizona State University's Biodesign Institute has been hunting for a biological Rosetta Stone -- an
enzyme2 allowing
DNA3's 4-letter language to be written into a simpler (and potentially more ancient)
molecule4 that may have existed as a
genetic5 pathway to DNA and RNA in the
prebiotic（生命起源以前的） world.
Research results, which recently appeared in the Journal of the American Chemical Society, demonstrate that DNA sequences can be
transcribed6 into a molecule known as TNA and reverse transcribed back into DNA, with the aid of commercially available
enzymes7.
The significance of the research is three-fold:
It offers tantalizing8（撩人的） clues about how DNA and RNA -- which encode the building plans for all earthly life -- may have arisen from more primitive9 information-carrying molecules10
Contributes to the field of exobiology（外空生物学） -- the search for alternative life forms elsewhere in the universe
Points to possible applications for TNA and other unusual nucleic acid molecules (known as xenonucleic acids or XNAs) in molecular11 medicine.
In the case of biomedical applications, XNAs may be developed into aptamers -- molecular structures that can
mimic12 the properties of naturally occurring polymers, folding into a variety of 3-dimensional forms and
binding13 with selected targets. Aptamers are useful for a range of clinical applications including the development of macromolecular drugs.
The
structural17 plans for organisms ranging from bacteria to
primates18 (including humans) are encrypted in DNA using an
alphabetic19 code consisting of just A, C, T & G, which represent the 4 nucleic acids. In addition to their information-carrying role, DNA and RNA possess two defining properties: heredity, (which allows them to propagate their genetic sequences to subsequent generations) and evolution, (which allows successive sequences to be modified over time and to respond to selective pressure).
The chemical
complexity20 of DNA has convinced most biologists that it almost certainly did not arise spontaneously from the prebiotic soup existing early in earth's history. According to one hypothesis, the simpler RNA molecule may at one time have held
dominion21 as the sole transmitter of the genetic code. RNA is also capable of
acting22 as an enzyme and may have
catalyzed23 important chemical reactions leading eventually to the first
cellular24 life.
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