An RNA condensate model for the origin of life

The RNA World hypothesis predicts that self-replicating RNAs evolved before DNA genomes and coded proteins. Despite widespread support for the RNA World, self-replicating RNAs have yet to be identified in a natural context, leaving a key 'missing link' for this explanation of the origin of life. Inspired by recent work showing that condensates of charged polymers can create electrochemical gradients capable of catalyzing hydrolysis, we consider a catalytic RNA condensate as a candidate for the self-replicating RNA. We develop a theoretical framework where an RNA condensate formed by the spontaneous demixing of disordered RNA sequences undergoes self-replicative amplification. Our theory addresses two central problems in the origins of life: (i) the origin of compartmentalization and (ii) the error threshold for the accuracy of templated replication. We show that many of the needed properties of this self-replicating RNA condensate have been realized experimentally in recent studies and can be formalized within a standard polymer physics framework. Specifically, we propose that short, low-complexity RNA polymers formed catalytic condensates capable of templated RNA polymerization. Because the condensate properties depend on the RNA sequences, RNAs that formed condensates with improved polymerization and demixing capacity would be amplified, leading to a 'condensate chain reaction' and evolution by natural selection. We believe this prediction could be tested with current experimental and theoretical tools. Furthermore, we note that the extant nucleolus appears to satisfy many of the requirements of an evolutionary relic for the model we propose. More generally, we suggest that future work on the origin of life would benefit from condensate-centric biophysical models of RNA evolution.