Further extracellular Darwinian experiments with replicating RNA molecules: diverse variants isolated under different selective conditions.

Experiments are described which demonstrate that it is possible to isolate in vitro a variety of mutant RNA molecules which exhibit qualitatively distinguishable phenotypes. The results suggest that precellular evolution could have involved selective forces of previously unsuspected diversity and subtlety. Suitable adjustment of the selective conditions leads to the isolation of variants optimally designed to compete successfully with the original viral nucleic acid. One of the properties that can be built into the variants is resistance to the presence of inhibitory analogues of the normal riboside triphosphates. Potentially, such variants could be used as antiviral devices in conjunction with the more usual chemotherapeutic agents.