Fig. 1.

Scheme for continuous evolution of ligase ribozymes. RNA and DNA are depicted as solid and open lines, respectively. Ligation of a chimeric DNA–RNA substrate by the ribozyme results in attachment of the T7 promoter sequence (prom) to the 5′ end of the ribozyme. Reverse transcription of reacted, but not unreacted, ribozymes results in the formation of a cDNA that serves as a template for transcription of multiple progeny RNAs.