What's Evolving in Wet A-Life?
Gerald F. Joyce
The Scripps Research Institute
Abstract
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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