Fig. 3.

Selection results for the MjPDT TRF library. Amino acid frequencies at the randomized sites were obtained by analysis of 24 functional MjPDT variants, which were isolated under stringent selection conditions (5 μg/ml tetracycline). The WT MjPDT gene was not recovered in this experiment, judging from the observed codons. Under nonselective conditions, the observed amino acid distribution at each position in the tripeptide motif was random. The WT residue at each of the randomized positions is indicated in parentheses.