Fig 4.

High-throughput chemical complementation screen. Active enzyme can be isolated from a pool of inactive mutants. The yeast selection strain was transformed with a 5:95 mixture of plasmids encoding the wild-type active cephalosporinase enzyme and the inactive Ser-64 → Ala cephalosporinase variant, respectively, and then plated onto an X-Gal indicator plate containing 10 μM Mtx-Cephem-Dex. Cells containing the active enzyme could be distinguished on the basis of the levels of X-Gal hydrolysis and hence lacZ transcription.