Bold claim first: a tiny 45-nucleotide RNA strand may unlock one of the biggest mysteries about life’s origins. A molecule like an RNA enzyme has been shown to perform two essential steps needed for self-replication, offering a fresh clue about how non-living chemistry on a prebiotic Earth could begin to copy itself and evolve.
Lead researcher Eduoardo Gianni, who collaborated with Philipp Holliger’s team at the University of Cambridge, explains that the two reactions do not occur in sequence and do not happen in a single reaction vessel yet. This means we’re not witnessing true self-replication, but a crucial demonstration of self-synthesis: the ability of an RNA to copy itself and to synthesize its complementary strand. Importantly, neither of these dual capabilities had been shown before for a polymerase ribozyme.
Polymerase ribozymes are RNA enzymes that provide the catalytic machinery central to the RNA world hypothesis. This theory suggests that life began with RNA molecules that could store genetic information and catalyze chemical reactions, eventually leading to cells that later adopted DNA and proteins. While modern life does not rely on ribozymes for replication, scientists have engineered them in the lab and found they can catalyze RNA synthesis. Still, natural ribozymes tend to be long and intricately folded, making spontaneous self-copying under prebiotic conditions seem unlikely.
Gianni notes that previous studies haven’t demonstrated true self-replication. Researchers have often assumed that complex prebiotic chemistry and non-enzymatic processes could drive the emergence of large, complex ribozymes. In response, his team took a bold step: they used directed evolution on a colossal library of about one trillion random RNA sequences to search for a new polymerase ribozyme lineage with a better shot at self-copying. The result is QT45, a 45-nucleotide ribozyme that shows both self-synthesis and the ability to replicate its own encoding strand.
Experiments conducted in eutectic ice—a slushy mix of water and salts that can promote polymerase activity and may resemble plausible prebiotic environments—demonstrated QT45’s dual capabilities. The ribozyme can build its complementary strand and can copy itself, though the yield for the copies was modest: about 0.2% after 72 days. Molecular biologist David Lilley from the University of Dundee describes this pace as extraordinarily slow, yet he acknowledges it as a meaningful proof-of-principle step toward validating the RNA world concept.
In an RNA-only origin scenario, shorter RNA fragments would be more plentiful than longer ones. Prior laboratory attempts at spontaneous RNA polymerization typically reached around 20 nucleotides, which could assemble into longer molecules like QT45. Gianni emphasizes that QT45 substantially lowers the non-enzymatic threshold necessary before ribozyme-catalyzed replication could take over, thereby increasing the estimated probability that life could emerge from chemistry alone.
Looking ahead, the researchers aim to perform the two reactions in a single reaction environment and complete a self-sustaining replication cycle. They also want to improve yields enough to support growth and evolution within the system.
Would you agree that this kind of progress makes the RNA world scenario more plausible, or do you think the remaining gaps still point to essential role for later biology (DNA and proteins) in the origin of life? Share your thoughts below.
