酶使DNA与外部细胞交换信息

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.   "TNA is resistant¹⁴ to nuclease degradation¹⁵, making it an ideal molecule for many therapeutic¹⁶ and diagnostic applications," Chaput says.   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 complexity^{20#p#分页标题#e#} 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.