Before DNA became Earth's primary genetic material, early forms of life are believed to have used RNA to encode genetic instructions. But what was doing the job before RNA came on the scene?
One suggestion has been AEG, a small molecule that when linked into chains forms a hypothetical backbone for peptide nucleic acids, which have been But there's been one drawback to this theory: until now, AEG has been unknown in nature.
Now, though, a team of American and Swedish scientists has discovered AEG within cyanobacteria - believed to be some of the most primitive organisms on Earth, and capable of living in extreme habitats, from hot springs to the Arctic tundra.
"Our discovery of AEG in cyanobacteria was unexpected," says Dr. Paul Alan Cox of the Institute for Ethnomedicine.
"While we were writing our manuscript, we learned that our colleagues at the Stockholm University Department of Analytical Chemistry had made a similar discovery, so we asked them to join us on the paper."
To find out just how widespread AEG production is among cyanobacteria, the scientists analyzed pristine cyanobacterial cultures from the Pasteur Culture Collection of Paris. They also collected samples of cyanobacteria from Guam, Japan, Qatar, as well as in the Gobi desert of Mongolia - and found that all of them produced AEG.
This naturally supports the idea that the earliest life on Earth may have done the same - but we should be cautious, says Cox.
Professor Leopold Ilag and his student Liying Jiang at Stockholm University's Department of Analytical Chemistry analyzed the same samples and came up with identical results: cyanobacteria produce AEG. While the analysis is certain, its significance for studies of the earliest forms of life on Earth remains unclear. Does the production of AEG by cyanobacteria represent an echo of the earliest life on Earth?
"We just don't have enough data yet to draw that sort of conclusion," he says. "However, the pharmaceutical industry has been exploring synthetic AEG polymers for potential use in gene silencing, so I suspect we have much more to learn."