Synthetic DNA and RNA has been shown to be capable of evolving in the lab, carrying hereditary traits with it.

The synthetic form of DNA, life's building block, was able to share information with real DNA and undergo directed evolution into biologically useful forms.

Boffins are studying the fundamental question about DNA: where did it come from?

One hypothesis is that DNA, which is built with deoxyribose sugars, evolved from the simpler form RNA, which is built from ribose sugars. But then the question becomes where did RNA come from?

"This is a big question," said John Chaput of Arizona State University. "If the RNA world existed, how did it come into existence? Was it spontaneously produced, or was it the product of something that was even simpler than RNA?"

To try to answer this question, Chaput joined a multidisciplinary team of scientists from England, Belgium and Denmark to develop synthetic DNA by replacing the sugars with six others to create XNA – xenonucleic acids. By experimenting with XNA, the team hopes to see if they can artificially create the NA that existed before RNA.

The only way all these changes from one step of NA to the next works is by having two generations of NA that can talk to each other.

The researchers were able to get their XNAs to talk to DNA by synthesising the specialised enzymes known as polymerases that are used to transfer information between RNA and DNA. This process ended up with polymerases that could transcribe and reverse-transcribe six different genetic systems: HNA, CeNA, LNA, ANA, FANA and TNA.

The boffins then started with a large pool of DNA sequences and used their polymerases to copy the information from their DNA library into an HNA. They were then able to get those HNA to undergo directed evolution into various forms by incubating it.

This advances the case for the pre-RNA hypothesis because it shows that an NA could have existed that like these XNAs which could fulfil a number of useful roles.

"Further down the road, through research like this, I think we'll have enough information to begin to put the pieces of the puzzle together," Chaput said. The paper was published in Science and was lead-authored by Philipp Holliger. ®