FIGURE 7.

Fitness profile of all evolutionary intermediates from the parent ribozyme (M0) to the M5 ribozyme (M5), at three selection pressures. A–C, intermediates are labeled according the their number of M5 mutations (M1, M2, M3, and M4). The selection pressures correspond to chloramphenicol concentrations of 10 μg/ml (A), 100 μg/ml (B), and 200 μg/ml (C). The fitness was measured as growth on medium containing the respective chloramphenicol concentration. The two M1 ribozymes that display significant growth are labeled (G9U and U239C). All evolutionary intermediates with the G9U mutation are shown in blue or green and connected by blue lines. Green symbols highlight the gatekeeper intermediates (see the “Results” section concerning Fig. 7, and see the third paragraph of the “Discussion”). The values for all intermediates at all selection pressures are given in supplemental Fig. S2. Error bars are S.D. from three biological experiments. D–F, corresponding heat maps: 10 μg/ml (D), 100 μg/ml (E), and 200 μg/ml (F). The arrangement of evolutionary intermediates is the same as in Fig. 6. Colors denote fitness values >0.6 (red), 0.6–0.3 (orange), 0.3–0.1 (yellow), and <0.1 (white).