Did RNA Develop in Linked Puddles?

The crucibles that bore out early building blocks of life may have been, in many cases, modest puddles.

Now, researchers working with that hypothesis have achieved a significant advancement toward understanding an evolutionary mystery -- how components of RNA and DNA formed from chemicals present on early Earth before life existed.

In surprisingly simple laboratory reactions in water, under everyday conditions, they have produced what could be good candidates for missing links on the pathway to the code of life.

And when those components joined up, the result even looked like RNA.

As the researchers' work progresses, it could reveal that much of the original chemistry that led to life arose not in fiery cataclysms and in scarce quantities, but abundantly and gradually on quiet, rain-swept dirt flats or lakeshore rocks lapped by waves.

In turn, their work could increase our understanding of the probability of life's existence elsewhere in the universe.

The research from the NSF/NASA Center for Chemical Evolution, headquartered at the Georgia Institute of Technology, is generously funded through a grant from the National Science Foundation and NASA. The recent results were published on April 25, 2016 in Nature Communications.

Pursuing the origins specifically of RNA, the close chemical relative of DNA, a research team led by Nicholas Hud, a professor in the School of Chemistry and Biochemistry at the Georgia Institute of Technology and director of the CCE, worked with a pair of potential chemical ancestors of the nucleobases of RNA.

For roughly half a century, scientists have hypothesized that life, which uses DNA to store genetic information, was preceded by life forms that used RNA very broadly. And RNA may have had a precursor, proto-RNA, with different but similar nucleotides (the "N" in RNA).

"Early Earth was a messy laboratory where probably many molecules like those needed for life were produced. Some survived and prospered, while others eventually vanished," Hud said. "That goes for the ancestors of RNA, too."

Using two molecules known as barbituric acid and melamine, the researchers formed proto-nucleotides so strongly resembling two of RNA's nucleotides that it is tempting to speculate that they are indeed their ancestors.

The two ingredients would have been readily abundant for reactions on a prebiotic Earth, Hud said. "And they would have been well suited for primitive information coding," he added.

Because of the resemblances and properties, some scientists already have speculated on an ancestral role for melamine and barbituric acid.

But the CCE scientists are careful not to jump to that conclusion just yet.

"To claim ancestry, we would have to show a mechanism by which these nucleotides we made in the lab could turn into the existing nucleotides in RNA," said Ram Krishnamurthy, Hud's collaborator from the Scripps Research Institute in La Jolla, California. "It's a complex path that we'd have to at least design on paper, and we're not there."

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