In a bid to figure out just how life first blossomed roughly 4 billion years ago, scientists have created an entirely new type of genetic replication system, producing molecules that can, in effect, self-replicate.
One of the most convincing arguments for how life started in the oceans is based around RNA, which is effectively a single strand of DNA. Similarly to DNA, RNA is made up of individual base pairs and can contain genetic information. It is thought that these molecules may be the precursor to DNA, and formed in deep-sea vents at the bottom of the oceans.
But in order for a piece of DNA – or in this case RNA – to replicate itself, it needs the assistance of enzymes. It has been found before that some strands of RNA can fold themselves into 3D shapes and form enzyme-like structures, known as ribozymes, and that these can successfully read and duplicate other strands of RNA.
The paradox, however, is that these ribozymes cannot read and duplicate themselves due to their folded structure, leading to something of a chicken and the egg scenario.
Now, for the first time, researchers say they have been able to develop a ribozyme that can replicate folded strands, including itself. This is a significant step towards understanding how the first life emerged in the oceans all those billions of years ago from just a blend of different molecules.
“We found a solution to the RNA replication paradox by re-thinking how to approach the problem – we stopped trying to mimic existing biology and designed a completely new synthetic strategy,” said Dr Philipp Holliger, co-author of the paper published in eLife. “It is exciting that our RNA can now synthesise itself.”
Strands of RNA are usually replicated by adding single base pairs one at a time. But the researchers tweaked this, to see what would happen if the ribozymes added three base pairs at a time instead. And what they found was pretty impressive.
While adding a single base pair made it impossible for the ribozyme to duplicate a folded piece of RNA, if the ribozyme was adding base pairs three at a time, the triplet would bond so tightly to the RNA it would begin to force it to unfurl, allowing it to be copied. This means that the ribozyme can replicate itself, thus solving the paradox.
The researchers suggest that if the “primordial soup” contained a muddle of base pairs of different lengths, then this could feasibly have helped kick-start life in the early oceans. While the researchers conducted this experiment at -7°C (19°F) to concentrate the RNA, they now want to explore whether they can achieve the same effect in a more chemically diverse mix, more similar to what the oceans would have been like when life began.
2