Artificial Life VI

What's Evolving in Wet A-Life?

Gerald F. Joyce
The Scripps Research Institute


The principles of darwinian evolution can be applied to a large, heterogeneous population of RNA or DNA molecules to obtain particular molecules that have desired biochemical properties, including the ability to catalyze a target chemical reaction. A population of variant molecules is subjected to repeated rounds of selective amplification in the test tube. Only those individuals that perform a chosen catalytic task are amplified so that, through successive rounds, the population adapts to the task at hand. Recently we developed the ability to carry out the in vitro evolution of RNA-based catalytic function in a continuous manner. The RNAs catalyze a ligation reaction that immediately makes them eligible for amplification and the newly-produced RNAs are immediately eligible to catalyze another reaction. This has enabled us to maintain laboratory ``cultures'' of evolving RNA enzymes, analogous to the way one maintains cultures of bacteria. The RNAs are perpetuated by a simple serial transfer procedure, amplifying indefinitely so long as an ongoing supply of substrate and other reaction materials is made available. During one run of continuous in vitro evolution, the RNA enzymes were amplified by a factor of 10E298 over 52 hours. By the end of this process, new ``generations'' of progeny RNA molecules were being produced approximately every 5 minutes.

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