A small piece of RNA copies itself, hinting at how life first began Premium

Scientists discover QT45, a self-replicating RNA molecule, offering insights into the origins of life on Earth.

In a 1953 experiment, two scientists named Stanley Miller and Harold Urey attempted to recreate the conditions of the early earth long before life existed. They showed that organic molecules such as amino acids, the building blocks of proteins, could form spontaneously in the conditions that prevailed on a primitive earth, 3.5-4 billion years ago.

While the experiment was revolutionary,  it did not settle the question of life’s origins. Critics pointed out that while amino acids could form, there was still no sign of genetic material, i.e. neither DNA nor RNA. Living organisms don’t merely contain proteins: they rely on genetic information encoded in DNA or RNA to build them. Demonstrating that proteins could arise was therefore only part of the story. 

Importantly, life must be able to produce more life. For that, a primitive system would need genetic information and also a way to copy that information. This created a problem. Usually, DNA or RNA stores instructions to make proteins called polymerases. These polymerases then copy the DNA or RNA so that, when a cell divides, each new cell receives a complete set of genetic information. It was and remains a classic chicken-or-egg problem.

Then, in the early 1980s, scientists discovered that RNA itself could perform simple chemical reactions, including being able to cut and paste pieces of itself. This discovery strongly shifted scientists’ thinking towards the possibility that RNA could have been the earliest genetic material on the primitive earth. If a single molecule could both store information and carry out chemical reactions, it could bypass the chicken-and-egg problem of needing proteins to copy genetic material. 

However, while scientists have already developed RNA molecules that could build other RNA molecules, they still lack an RNA that could copy the information contained within itself. The difficulty was structural: the RNA enzymes capable of copying other RNAs were large and complex — between 150-300 nucleotides — and in trying to fold into their functional shapes they could not easily serve as templates for their own replication. In other words, RNA could help other proteins replicate but couldn’t self-replicate.

Now, however, in a paper in Science, scientists from the MRC Laboratory of Molecular Biology in the U.K. have reported that they have generated a self-replicating RNA molecule. Specifically, the researchers produced a small RNA molecule, just 45 nucleotides long, that could copy its own genetic information.