Figure 4.

Nucleotide substitutions in the evolved fucosidase gene. The predicted amino acid changes are shown above the gene by the single-letter denotation, numbered according to the wild-type β-galactosidase sequence (17). Amino acid changes in the N-terminally fused peptide region (hatched area) are indicated by small vertical arrows. Mutations that do not result in amino acid changes are shown below the gene, numbered starting at the HindIII site, as in the parental plasmid pCH110. The gpt promoter is indicated by a thick arrow. The positions of the known active site residues of the wild-type β-galactosidase are indicated by black bars.