Highly Efficient Self-Replicating RNA Enzymes

• An optimized self-replicating RNA enzyme was obtained by directed evolution
• The enzyme undergoes sustained exponential growth with a doubling time of 5 min
• Amplification of 10100-fold was achieved over a period of 37.5 hr
• The optimized enzyme will enable more complex synthetic genetic systems

SummaryAn RNA enzyme has been developed that catalyzes the joining of oligonucleotide substrates to form additional copies of itself, undergoing self-replication with exponential growth. The enzyme also can cross-replicate with a partner enzyme, resulting in their mutual exponential growth and enabling self-sustained Darwinian evolution. The opportunity for inventive evolution within this synthetic genetic system depends on the diversity of the evolving population, which is limited by the catalytic efficiency of the enzyme. Directed evolution was used to improve the efficiency of the enzyme and increase its exponential growth rate to 0.14 min−1, corresponding to a doubling time of 5 min. This is close to the limit of 0.21 min−1 imposed by the rate of product release, but sufficient to enable more than 80 logs of growth per day.

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