FIGURE 3.

Secondary structure representations of the mutations identified after 14 rounds of evolution in each of the four lines. Note that these mutations reflect the most active ribozymes after two rounds of enrichment at high selection pressure (rounds 13 and 14). The line (I–IV) is given for each secondary structure. For each structure, 10 sequences were analyzed. The color of the nucleotide corresponds to the frequency with which the nucleotide was found mutated: red, 8–10 mutations; green, 5–7 mutations; blue, 2–4 mutations; black, 0–1 mutation. See Fig. 1 for explanations on the secondary structure. The positions of the P6b stem-loop, P9.2 stem-loop, and the 5′-duplex are indicated. Note that the mutations in the P6b loop are highly enriched in lines II and IV but not in lines I and III.