A “huge” experiment shows how life originated on Earth

Did life on Earth arise from copies of RNA itself? A research team is tracking this scenario in the laboratory.

One widely discussed theory suggests that the primordial soup only contained the potential for life about 4 billion years ago, long before dinosaurs or even bacteria appeared. Then a molecule called RNA took a dramatic step into the future: it made a copy of itself, then the copy made another copy, and over millions of years, RNA gave birth to DNA and proteins, which together formed a cell, the smallest unit of life capable of surviving on its own.

Now, scientists at the Salk Institute for Biological Studies in La Jolla, California, have put a small but essential part of the story into action, taking an important step toward proving the RNA world theory. In test tubes, they developed an RNA molecule capable of making exact copies of another type of RNA.

The work that In the magazine Proceedings of the National Academy of Sciences published It 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 work. “This is how life could arise in the laboratory or anywhere in the universe.”

The team is still far from proving that life on Earth actually arose in this way, but the scenario they tested likely mimics one of the first beginnings of evolution, a concept proposed by English naturalist Charles Darwin more than 150 years ago and described years ago. “This is a starting point for understanding how life evolved,” says Nikolaos Papastavrou, lead author of the study and a postdoctoral researcher at Salk University.

No more faded copies

To reach this point, scientists have overcome perhaps the biggest obstacle to the plausibility of the RNA world theory. Until now, no RNA molecule in the laboratory has been able to create copies of other RNA that are precise and efficient enough.

The RNA molecule must create copies that are 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 malfunctioning camera producing a blurry or faded version of the image. If you put the faded copy into the machine, a new copy that is even worse will be created.

“If the error rate is very high, you can [genetische] “The information is no longer available,” Joyce said. Mistakes happen too quickly for Darwinian selection to select winners best equipped to survive, and “round after round of evolution sees populations disintegrating in no man’s land.”

Without room for error, RNA cannot adapt

Even if the transcription has to be very good, it cannot always be literally correct. Without a margin for error, RNA would not be able to adapt to a changing environment, as organisms must in the wild. For example, imagine a hairless sphinx cat trying to survive as temperatures drop and the world heads into a new ice age. In this unlikely scenario, the cat will have to change its hairless nature as soon as possible.

In the new work, Salk scientists created an RNA that makes copies of so-called hammerhead RNA. Instead of copying other RNA molecules, hammerhead RNA cuts them up. When RNA made copies of the hammerhead, each new generation was still able to tear it apart; Each generation was also easier to copy.

John Chabot, a professor of pharmaceutical sciences at the University of California, Irvine, who was not involved in the study, described the Salk team's crossing of that threshold as “huge,” adding, “At first I thought it was a bit astonishing.” Poetry. …He's so cute.

“A major step forward for the RNA world theory.”

To show that their RNA was better at copying, the Salk team tested the 71st generation copy against one of their distant ancestors. The newest generation has surpassed their predecessors when it comes to creating accurate copies. “Overall, I think this is a big step forward for the theory of the RNA world,” 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 studying the origin of life for a decade, emphasized that “the field has become a little broader” by imagining a beginning in which there was not only RNA but also other building blocks of life. Other building blocks can include lipids, which are part of cell membranes, amino acids, and organic compounds found in proteins.

In this alternative scenario, Bonfieu says, 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 that it is in [Ur-]Maybe there was more to it than just RNA. RNA-based evolution may have begun in lipid fractions, on mineral surfaces, or in association with other molecules.

The central point, Joyce says, is that “at some point Darwinian evolution began,” and early in the history of life, ribonucleic acid (RNA) performed the crucial tasks of storing genetic information and speeding up the chemical reactions needed to make copies of genes. This information.

How to control development

Michael Kay, a professor of biochemistry at the University of Utah, described the new work as a “very exciting advance” that provides “important clues” to the RNA world theory. [liefert]Which shows that it is plausible and plausible.” He added that the RNA transcriptase developed at Salk “will be a valuable tool for people who want to conduct directed evolution experiments.”

Directed evolution, sometimes called test tube evolution, is a laboratory procedure that allows scientists to mimic evolution by passing molecules from generation to generation so that the molecules receive improvements that help them survive.

Although the experiments in the new work took two years, it took Joyce and his colleagues nearly 10 years to pave the way and patiently grow RNA molecules generation after generation. If scientists succeed in creating RNA that can copy itself, evolution could largely happen on its own.

“All we have to do is feed them the four building blocks continuously,” Joyce says. Like DNA, RNA consists of four chemical bases, three of which are homologous: adenine, cytosine, and guanine. The fourth building block of RNA is the uracil base, while the fourth building block of DNA is thymine. The laboratory version of evolution would 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 them,” Joyce says. “Once evolution starts on Earth, look at the amazing things they invented,” he said.

We are currently testing machine translations. This article was automatically translated from English to German.

This article was first published in English on March 9, 2024 on “washingtonpost.com” was published as part of the collaboration, and is now also available in translation for readers of the IPPEN.MEDIA portals.