A 'huge' experiment suggests how life began on Earth

Now, an important advance supports this RNA world theoryScientists at the Salk Institute for Biological Studies in La Jolla, California, tell a small but essential part of the story. In test tubes, they are Phase of the RNA molecule Which was able to make precise copies of a different type of ribonucleic acid (RNA).

This work, published in the journal Proceedings of the National Academy of Sciences, brings them closer to the big goal of growing an RNA molecule that makes exact copies of itself.

“Then he would be alive,” said Gerald Joyce, president of Salk and one of the authors of the new paper. “So, this is the path to how life could arise in the laboratory, or, in principle, anywhere in the universe.”

The team is still far from proving that this is how life on Earth really began, but the scenario they propose is that this is how life on Earth began It likely mimics one of the oldest movements of evolution, a concept described by English naturalist Charles Darwin more than 150 years ago.

“It's a stepping stone toward understanding how life evolved,” says Nikolaos Papastavrou, first author of the paper and a postdoctoral fellow at Salk.

To get to this point, scientists have overcome the biggest obstacle to the plausibility of the RNA World theory. Until now, no RNA molecule in the laboratory has succeeded in making copies of other RNA that are accurate and efficient enough.

The RNA molecule must make copies very close to the original to achieve the same delicate balance that governs Darwinian evolution in nature. If the transcripts change too much, the RNA's capabilities deteriorate, and things go downhill quickly. Imagine a faulty camera that creates a fuzzy or blurry version of an image. When put into the machine, the mysterious copy produces a new, worse copy.

“If the error rate is too high, you won't be able to sustain [genetic] “Information,” Joyce said. “It just explodes.” Mistakes happen too quickly to allow Darwinian selection to choose the winners, those best equipped to survive, and “round after round of evolution sees the population dissipating into no man’s land.”

Although the transcription should be very good, it cannot be perfect all the time. Without room for error, RNA would not be able to adapt when its environment changes, as organisms do in the wild. Imagine, for example, a hairless sphinx cat trying to survive as temperatures drop and the world heads toward a new ice age. In this unlikely scenario, the cat will need to change its hairless nature quickly.

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In the new work, Salk scientists created an RNA that makes copies of so-called hammerhead RNA. Instead of copying other RNA molecules, the hammerhead cuts them up. When RNA made copies of the hammerhead, each new generation could still cut; Copying each of them has also become easier.

John Chabot, a professor of pharmaceutical sciences at the University of California, Irvine, who was not involved in the study, called the Salk team's crossing of that threshold “huge,” adding that “at first, I looked at it as a bit of a big deal.” A little jaw dropping. …It's very elegant.”

To show that their RNA was better at copying, the Salk team tested a copy of the 71st generation against one of its distant ancestors. The latest generation has outperformed its predecessor when it comes to making accurate copies.

“Overall, I think it's a great step forward” for the RNA World theory, said Claudia Bonvieux, a junior group leader at the University of Strasbourg in France, who was not involved in the study.

Bonfieu, who has been researching the origins of life for the past decade, stressed that “the field has become a bit more expansive” by imagining a beginning in which not only RNA existed, but other building blocks of life as well. the others They can include lipids, which are part of the cell membrane, amino acids, and organic compounds found in proteins.

In this alternative scenario, Bonfieu said, the different building blocks reside in chambers in a kind of primitive version of a cell.

In an email response, Joyce said: “I agree with Claudia's point that there may be more to it [primordial] A soup of just RNA. RNA-based evolution may have begun within lipid compartments, on mineral surfaces, or in association with some other molecules.

The central point, Joyce said, is that “Darwinian evolution eventually came into play,” and at some point early in the history of life, ribonucleic acid (RNA) played the crucial roles of retaining genetic information and speeding up the chemical reactions needed to make copies. from that information. .

Michael Kay, a professor of biochemistry at the University of Utah, called the new study “a very exciting advance” that gave the RNA scientist theory “a key piece of evidence.” [to show] “It is reasonable and reasonable.” He added that the RNA transcriptase developed at Salk “will provide a valuable tool for people who want to conduct directed evolution experiments.”

Directed evolution, sometimes called test tube evolution, is a laboratory process that allows scientists to mimic evolution by directing molecules from one generation to the next, enabling the molecules to gain improvements that help them survive.

Although the experiments in the new paper took two years, it took Joyce and his colleagues nearly 10 years to pave the way, patiently turning up generation after generation of RNA molecules.

If scientists succeed in producing RNA that can copy itself, evolution could largely continue on its own.

“All we have to do is provide it with a constant supply of the four essential elements,” Joyce said. RNA, like DNA, consists of four chemical bases, three of which are homologous to both: adenine, cytosine, and guanine. For the fourth component, RNA contains the base uracil, while the fourth component in DNA is thymine.

The laboratory version of evolution will allow RNA molecules to adapt as scientists change temperature or environment.

“The most fun thing is introducing new chemicals that go beyond the four bases in RNA and seeing what evolution can do with those bases,” Joyce said.

“Once evolution started on Earth, look at all the amazing things they invented,” he said.