Hauf, S.; Nakamura, R.; Cellini, B.; Yokobayashi, Y.; Dindo, M.

The emergence of the first catalytically active biopolymers remains a scientific mystery. Some abiotic chemistries for the formation of precursor molecules to biopolymers -- such as nucleotides and amino acids -- are known. However, abiotic polymerization usually results in short polymers of only a few units in length. This is too short for meaningful information storage or catalytic activity, a limitation known as the Flory Length Problem. Additionally, the first biocatalysts presumably had low activity because they were generated by random polymerization. Therefore, enrichment of substrates and catalysts seems necessary for significant rates of catalysis to occur. Could RNA phase separation be a solution to these challenges? Our experimental evidence demonstrates that at acidic pH, short RNAs (<20 nt) readily phase-separate into a condensed phase enriched with longer RNA fragments, primarily through phosphate backbone protonation. These RNA condensates stably compartmentalize RNA and DNA species without rapid flux of genetic material, maintaining their identity over extended periods even in the absence of membranes. In addition, the RNA phase concentrates ions critical for RNA folding and activity, along with small organic molecules, phospholipids, peptides, ribozymes, and large proteins. Beyond enriching diverse components, RNA condensates function as microreactors with dual catalytic capabilities. They physically enhance reaction rates by concentrating reactants within a confined space and simultaneously act as inherent catalysts that directly facilitate chemical transformations. These condensates also support ribozyme and enzymatic activity. Collectively, these findings suggest that RNA phase separation may have played a crucial role in lifes origins by providing spatial compartmentalization, inherent catalytic activity, and biopolymer enrichment, particularly of potentially longer catalytic species.