Figure 1.

Trajectory for amp^R activity during 50 rounds of directed evolution. Each point represents the ampicillin concentration at which the screening was done. To set the ampicillin concentration for a given screening, JM109 cells were transformed with a plasmid mix obtained from the previous round of screening, and the cell growth was examined at various concentrations of ampicillin. At every round, the screening was done at as high an ampicillin concentration as possible. At the 14th round (arrow head), IPTG was omitted from the medium. At the 15th round (asterisk), the vectors were changed from a very high-copy plasmid, pHSG398, to a moderately high-copy plasmid, pBR322.