Figure 3.

(A) Colonies of E. coli HB101 cells that were transformed with the active- or inactive-ribozyme-expression plasmid. In the presence of 70 μg/ml TMP, colonies expressing active ribozymes (Left) grew faster than colonies expressing inactive ribozymes (Right). The difference in growth rates between the active- and inactive-ribozyme-expressing colonies was greater at 27°C (Upper) than at 37°C (Lower). (B) Distribution of colonies according to their colony size. About 4000 colonies that appeared in A were classified into 11 classes based on the diameter of colonies. The difference in growth rates between the active- and inactive-ribozyme-expressing colonies was greater at 27°C (Left) than at 37°C (Right). Since the E. coli strain HB101 used in this study produces a low level of endogenous DHFR, formation of background colonies could not be avoided.