Scientists have proposed a new model that describes how ancient RNA molecules may have acquired the ability to cut themselves. This self-cutting ability, or self-cleavage, is considered crucial for the evolution of RNA-based life before the emergence of proteins and DNA. The model, presented in the journal Nature Chemistry, sheds light on the chemical processes that could have led to the origin and diversity of ribozymes, RNA molecules that can act as catalysts.

Ribozymes are essential components of the RNA world hypothesis, which suggests that RNA preceded proteins as the primary information-carrying and catalytic molecules in early life. These RNA molecules would have needed the ability to self-cleave in precise locations to regulate their own replication, processing, and function.

The new model, developed by researchers from the Okinawa Institute of Science and Technology Graduate University (OIST) in Japan, proposes that self-cleavage could have emerged from the interaction between RNA molecules and simple chemical species, such as metal ions and small organic molecules, in a prebiotic environment.

"We propose that RNA self-cleavage could have originated from non-enzymatic reactions, driven by the chemical reactivity of RNA itself, coupled with the assistance of metal ions and other small molecules that were abundant in the prebiotic Earth," explained corresponding author Dr. Ryuichi Masui, a team leader at OIST's Precursory Chemistry Unit.

The model suggests that certain RNA sequences, called hairpin ribozymes, could have self-cleaved through a specific chemical reaction called a transesterification reaction. This reaction involves the transfer of a phosphate group from one RNA molecule to another, resulting in the cleavage of the RNA backbone.

The researchers tested their model using synthetic RNA molecules and found that the presence of metal ions, such as magnesium or calcium, significantly enhanced the rate of self-cleavage in hairpin ribozymes. They also identified a small organic molecule, imidazole, which further accelerated the self-cleavage reaction.

According to the model, these prebiotic chemical species could have acted as catalysts, promoting the self-cleavage of RNA molecules and facilitating the evolution of more complex and diverse ribozymes.

The findings provide new insights into the origin of catalytic RNA molecules and offer support for the RNA world hypothesis. The study highlights the potential role of non-enzymatic reactions, metal ions, and small organic molecules in the emergence of self-replicating and functional RNA systems in the early stages of life's evolution.

"Our model suggests that the self-cleavage of RNA could have arisen from simple chemical processes, setting the stage for the emergence of more complex RNA molecules and eventually leading to the origin of life," concluded Dr. Masui.