The building blocks of DNA and RNA could have appeared together before the start of life on Earth

For the first time, scientists have found strong evidence that RNA and DNA could come from the same set of precursor molecules even before life evolved on Earth there are about four billion years.

The discovery, published on April 1 in Nature Chemistry, suggests that the first living beings on Earth may have used both RNA and DNA, as all cell-based life forms currently do. In contrast, the prevailing scientific view – the "RNA world" hypothesis – is that early life forms were based solely on RNA and evolved only later to make and use DNA. .

"These new findings suggest that it may not be reasonable for chemists to draw on RNA World's hypothesis to investigate the origins of life on Earth," says co-principal investigator Ramanarayanan Krishnamurthy. Ph.D., associate professor of chemistry. at Scripps Research.

Krishnamurthy and his lab have been working on the study with John Sutherland's laboratory, DPhil, of the Molecular Biology Laboratory of the British Council for Medical Research in Cambridge, as part of the Simons Collaboration on the Origins of Life. Foundation, based in New York.

RNA (Ribonucleic Acid) and DNA (Deoxyribonucleic Acid) are chemically very similar, but chemists have never been able to show how one could have been converted into L & rdquo; Another on the primitive Earth, without the help of enzymes produced by primitive organisms. In part because of this lack of a chemical pathway proving pre-life or "pre-biotic" linking RNA to DNA, researchers in this area tend to think that RNA, simpler and more versatile, was at the base of the first. life forms – or at least at an early stage of life before the emergence of DNA. RNA is able to store genetic information like DNA can, is able to catalyze biochemical reactions such as protein enzymes, and otherwise could probably have performed the basic biological tasks that would have been required in the early forms of life.

Although researchers of the origin of life in recent decades have largely adopted the RNA World hypothesis, Sutherland, Krishnamurthy, Harvard's Jack Szostak and others have accumulated evidence that RNA and DNA may have appeared more or less simultaneously in early life forms. .

In a study published in 2017, for example, Krishnamurthy and colleagues at Scripps Research identified a plausibly present compound on the pre-biotic Earth that could have fulfilled the crucial task of linking RNA building blocks. in larger strands of chain RNA, and could have done the same thing for the building blocks of DNA and proteins.

In the new study, scientists combined the results of this survey with recent discoveries by Sutherland and his lab on a compound called thiuridine. The latter was probably present on Earth before life, and could have been a chemical precursor to the nucleoside building blocks of the first RNAs. The team has shown that in a few chemical reaction steps, which would presumably have occurred in a pre-biotic world, it could convert this precursor from a constitutive RNA block into a constitutive block of DNA – the deoxyadenosine, which forms the letter "A". in the modern four-letter DNA code. Alternatively, they could convert thiouridine to deoxyribose, which is very close to deoxyadenosine and may also have been a precursor to early building blocks of DNA.

This discovery should allow scientists to more easily accept the possibility that DNA and RNA grow together and be included in early life forms. Some researchers, including Sutherland, have suggested that RNA and DNA would have even been blended to form the first genes. It is not known that such an organism occurs naturally at the present time, but a recent article by Peter Schultz, Ph.D., Scripps Research and their colleagues have described a modified bacterium that can survive with genes consisting of a mixture of RNA and DNA.

Krishnamurthy suspects that, regardless of life, RNA and DNA, with their respective strengths and weaknesses, would have quickly fallen into the rather strict division of labor observed in all cells today. hui: the DNA for stable long-term storage of genetic information and RNA for its own set of tasks, including the storage and short-term transport of genetic information and the manufacture of proteins .

"There is the beginning of an awareness on the ground that RNA and DNA could have been mixed initially and subsequently separated according to what they do." better, "said Krishnamurthy.

The authors of the study, "Prebiotic phosphorylation of 2-thiouridine provides nucleotides or building blocks of DNA via photoreduction," were Jianfeng Xu, Nicholas Green and John Sutherland of MRC, and Clémentine Gibard and Ramanarayanan Krishnamurthy of Scripps.