Fig. 3.

Response curves of wt MerR and the Cd-specific MerR mutants found after the first and second mutation rounds. (a) wt MerR. (b) Vector with wt MerR deleted from the reporter gene plasmid. The curve shows continuous expression of the firefly luciferase gene from MerOP. The MerR mutants obtained after the first mutagenesis round were A_D23 (c) and A_D24 (d), and those obtained after the second mutagenesis round were B_D20 (e), B_DB4 (f), B_DB10 (g), B_DB17 (h), B_DB26 (i), B_DB27 (j), B_DB29 (k), and C_DB21 (l). The responses to HgCl₂ and CdCl₂ are shown for wt MerR and the MerR mutants; the detected responses to other metals are shown, while negative results are omitted.