Life began small, but even the tiniest cells need a way to copy their instructions. A new laboratory system shows that a simple set of RNA building blocks can get most of the way there, pushing experimental biologists closer to watching life’s opening act unfold in a test tube.
“This was the molecule that ran biology,” said James Attwater of University College London, who led the study.
The work centers on an artificial ribozyme that joins three‑letter chunks of RNA while cycling between hot, cold, acidic, and alkaline conditions.
The idea that one molecule once carried both genetic information and catalytic power, dubbed the RNA world, was first laid out almost 40 years ago.
Modern cells still hint at that past because ribosomes, spliceosomes, and many regulatory switches all rely on RNA to keep genes working.
Short RNA strands can fold into active shapes, cut other RNAs, and even build peptides, making them plausible ancestors of today’s enzymes. Researchers have spent decades trying to show that RNA can also copy itself fast enough to allow Darwinian evolution.
Copying RNA sounds easy until you meet the strand separation problem. Freshly made daughter strands cling so tightly to their templates that the double helix cannot unwind in time for another round of replication.
Some groups have used heat, acid, crowding agents, or helper oligonucleotides to pry the strands apart, but each fix either damages RNA or stalls the copying chemistry. Freeze-thaw studies showed that ice concentrates reactants without cooking them, hinting at a gentler route.
Attwater’s team discovered that short trinucleotide triphosphates bind single strands strongly enough to stop them from re‑zipping while also doubling as substrates for extension. Three bases form a sweet spot: long enough to grip, yet short enough to avoid frequent errors.
Under pH swings that first melt duplexes at 176 °F, then freeze them at 19 °F, the ribozyme weaves the triplets into fresh complementary strands. So far the enzyme can copy thirty of its 180 letters before running out of steam, but the researchers see clear paths to speedup.
During each cold phase, the remaining liquid between ice crystals becomes a concentrated eutectic phase where magnesium ions, the ribozyme, and triplets are corralled together.
In that micro‑brine the polymerase connects the triplets, then waits for the next heat pulse to start another cycle.
“There might be a relationship between how biology used to copy its RNA and how biology uses RNA today,” noted Attwater.
The group watched exponential gains when they put the system through repeated hot-cold swings, confirming that templates made in one cycle feed the next.
“RNA nucleotide triplets serve very specific informatic functions in translation in all cells,” noted Zachary Adam, a geochemist at the University of Wisconsin‑Madison who was not involved in the study.
The binding preference of GC‑rich triplets echoes the stability pattern of codons that still anchor the genetic code.
The experts found that the triplets most able to keep strands apart match those believed to seed the earliest triplet code. This overlap suggests that replication chemistry could have nudged evolution toward the codon system long before proteins appeared.
Models of primordial ponds often invoke hot springs that swing between acidic jets and freezing spray, conditions seen in Iceland today.
Such locales supply the freshwater and rapid pH shifts that the triplet mechanism needs, making the scenario geologically plausible.
The system didn’t just copy preexisting templates. It also generated new RNA sequences from random starting material and then amplified those fragments through multiple rounds.
Some of the strongest amplification came from strands resembling parts of the ribozyme itself, suggesting early self-copying behavior that could foreshadow how functional sequences emerged billions of years ago.
To cross the finish line, the ribozyme must copy its entire 180‑letter body and then repeat the feat indefinitely. Attwater’s team is engineering faster variants and trimming unnecessary folds to lighten the enzymatic load.
If full self‑replication emerges, chemists can finally watch mutation and natural selection operate in a test tube filled with nothing but RNA and simple salts.
The achievement would turn a long‑standing hypothesis into an observable process, offering the clearest window yet on life’s origin.
The study is published in the journal Nature Chemistry.
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