Fig. 1.

A schematic description of the experimental system. TEM-1 β-lactamase was transcribed from plasmid TEM-1-pET27 under a T7 promoter. To enable the transcription of TEM-1, wild-type T7 RNA polymerase, or a mutant that exhibits ≈20-fold higher rate of transcriptional errors (mutator T7 RNAP) were expressed from plasmid pACYC-T7. TEM-1 transcripts carrying mutations resulted in mutated enzyme molecules, and reduced levels of ampicillin resistance. The reproduction of single transcripts and their encoded TEM-1 molecules was achieved by reverse transcription and PCR amplification (RT/PCR) to obtain cDNAs that were subsequently cloned and individually analyzed.