Figure 2.

Improvement of RNA ligase activity over successive rounds of in vitro selection. Self-ligation rates were measured for the population as a whole at 30°C, as described in Materials and Methods. Calculated ligation rates are based on the first 2% of the reaction. Mutagenic PCR was performed after rounds 4 and 6. After round 5, the 5′ stem–loop of the ribozyme was changed and the concentration of KCl was decreased from 400 to 50 mM.