Climbing Darwin's ladder

The work of Bartel and Szostak, in which RNA molecules were selected to enhance the ability to catalyze a reaction similar to a step in protein-catalyzed RNA replication, is discussed. An important aspect of this experiment was the ability to reach a high level of functional organization in ten evolutionary steps. Further steps necessary to obtain an RNA enzyme with RNA replicase activity include performing the reaction with mononucleoside 5'-triphosphates, generalizing the reaction to include a variety of sequences without loss of template-dependent specificity, and overcoming template self-structure that could prevent some regions from being copied efficiently.