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The theory of the origin of life involving RNA-protein hybrids is gaining new support

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The theory of the origin of life involving RNA-protein hybrids is gaining new support

Chemists say they have solved a crucial problem in early life theory by demonstrating that RNA molecules can bind short chains of amino acids together.

Conclusions published on May 11 Naturesupport option on Hypothesis “World of RNA”.which suggests that before the evolution of DNA and the proteins it encodes, the first organisms were based on RNA chains, a molecule that can both store genetic information – in the form of nucleoside sequences A, C, G and U – and act as a catalyst for chemical reactions .

The discovery “opens wide and fundamentally new ways to find early chemical evolution,” said Bill Martin, who studies molecular evolution at the Heinrich Heine University in Dusseldorf, Germany.

In the RNA world, according to standard theory, life could exist in the form of complex proto-RNA chains capable of both copying themselves and competing with other strands. Later, these “RNA enzymes” could develop the ability to build proteins and eventually transfer their genetic information into more stable DNA. How exactly this could have happened was an open question, in part because catalysts made from RNA alone are far less effective than the protein-based enzymes found in all living cells today. “Although [RNA] catalysts have been discovered, their catalytic power is poor, ”said Thomas Karel, an organic chemist at Ludwig Maximilian University in Munich in Germany.

RNA ribosomes

Exploring this puzzle, Karel and his colleagues were inspired by the role that RNA plays in how all modern organisms build proteins: the RNA chain that encodes a gene (usually copied from a DNA sequence) runs through a large molecular machine called a ribosome that builds a corresponding protein on one amino acid.

Unlike most enzymes, the ribosome itself is made up not only of proteins but also of RNA segments – and they play an important role in protein synthesis. Moreover, the ribosome contains modified versions of the standard RNA nucleosides A, C, G and U. These exotic nucleosides have long been considered as possible remnants of the original broth.

Karell’s team built a synthetic RNA molecule that included two such modified nucleosides by combining two pieces of RNA commonly found in living cells. At the first of the exotic sites, the synthetic molecule could bind to an amino acid, which then moved sideways to bind to the second exotic nucleoside adjacent to it. The team then separated their original RNA chains and introduced a fresh one that carries its own amino acid. It was in the right position to form a strong covalent bond with the amino acid previously attached to the second strand. The process continued step by step, growing a short chain of amino acids – a mini-protein called a peptide – that attached to RNA. To form bonds between amino acids requires energy, which researchers provide by priming amino acids with various reagents in solution.

“This is a very exciting discovery,” says Martin, “not only because it identifies a new pathway for the formation of RNA-based peptides, but also because it opens up new evolutionary significance for naturally modified RNA bases.” The results point to the important role that RNA plays in the origins of life, but not requiring only RNA for self-replication, Martin adds.

Lauren Williams, a biochemist chemist at the Georgia Institute of Technology in Atlanta, agrees. “If the origin of RNA and the origin of protein are interrelated, and their appearance is not independent, then mathematics will radically shift in favor of the RNA-protein world and from the world of RNA,” he says.

To show that this is a plausible origin of life, scientists need to follow a few more steps. The peptides formed on the RNA team consist of a random sequence of amino acids, not one that is determined by the information stored in the RNA. Karel says that larger RNA structures may have regions that form into shapes that “recognize” certain amino acids at specific sites, creating a well-defined structure. And some of these complex RNA-peptide hybrids may have catalytic properties and be subjected to evolutionary pressure to become more efficient. “If a molecule can replicate, you have something like a mini-organism,” Karel says.

This article is reproduced with permission and has been first published May 11, 2022.

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