From “Simpler Times: Did an Earlier Genetic Molecule Predate DNA and RNA?” (ScienceDaily, Jan. 9, 2012), we learn,
According to Chaput, one interesting contender for the role of early genetic carrier is a molecule known as TNA, whose arrival on the primordial scene may have predated its more familiar kin. A nucleic acid similar in form to both DNA and RNA, TNA differs in the sugar component of its structure, using threose rather than deoxyribose (as in DNA) or ribose (as in RNA) to compose its backbone.
In an article released online January 9 in the journal Nature Chemistry, Chaput and his group describe the Darwinian evolution of functional TNA molecules from a large pool of random sequences. This is the first case where such methods have been applied to molecules other than DNA and RNA, or very close structural analogues thereof. Chaput says “the most important finding to come from this work is that TNA can fold into complex shapes that can bind to a desired target with high affinity and specificity.” This feature suggests that in the future it may be possible to evolve TNA enzymes with functions required to sustain early life forms.
… research has now shown that a single strand of TNA can indeed bind with both DNA and RNA by Watson-Crick base pairing — a fact of critical importance if TNA truly existed as a transitional molecule capable of sharing information with more familiar nucleic acids that would eventually come to dominate life.
In “Before DNA, before RNA: Life in the hodge-podge world”(New Scientist, 08 January 2012), Michael Marshall notes
That doesn’t mean TNA was the original genetic material, though. Chaput thinks it probably wasn’t, if only because the chemistry of early Earth was so messy that TNA would not have arisen on its own. Rather, many different kinds of genetic material probably formed in a genetic hodge-podge. “The most likely scenario is that nature sampled lots of different things,” says Chaput.
Hmmm. What is “nature” that it should be doing any sampling?
Also,
… there are problems with the hodge-podge world hypothesis. For one thing, there is no trace of TNA or its cousins in modern organisms. For another, although TNA looks simpler than RNA, we can’t be sure it was easier to make some 4 billion years ago because no one has actually made it in the conditions that existed on Earth before life began, says John Sutherland of the MRC Laboratory of Molecular Biology in Cambridge, UK.
TNA has also not been found in life forms today, which is why the media release reads “ if TNA truly existed as a transitional molecule capable of sharing information with more familiar nucleic acids that would eventually come to dominate life.” You be the judge.