Figure 1

Position of neutral mutations in the E. coli β-glucuronidase. The gusA gene was subjected to four rounds of neutral screening in which 1815, 801, 1341, and 952 blue (gusA⁺) colonies were selected respectively. The fourth round neutral library was then screened for β-galactosidase activity. The five residues where mutations contributed to galactosidase activity identified in this study and previously are shown in red. Neutral mutations identified in the neutral screen are shown in yellow. Mutations that were identified in the galactosidase screen but did not contribute significantly to galactosidase activity are shown in blue. The E. coli β-glucuronidase sequence was modelled on to the human glucuronidase structure [26], using Swiss-Model [27, 28].