Fig. 3

Complementation of ΔmetAB with metX/Y gene pairs. (A) Schematic illustration of the synthetic metYX operon on a low-copy plasmid used to complement ΔmetAB. A synthetic operon consisting of the metY and metX genes was constructed by adding a synthetic constitutive promoter, a ribosome binding site (RBS) for each gene, and a synthetic terminator. Restriction sites were included to facilitate rearrangement and analysis of mutant genes. (B) Growth curves of the complemented ΔmetAB strains on a minimal MOPS medium. WT: E. coli MG1655; ΔmetAB: WT with deletion of the metAB genes; ΔmetAB-DG/CM/LI/CG: ΔmetAB complemented with a pCCl plasmid expressing metX and metY of the indicated bacterial strain. ΔmetAB-AB: WT with deletion of the metAB genes complemented with a pCCl plasmid expressing E. coli’s metA and metB. (C.) Growth of the complemented ΔmetAB strains on a MOPS minimal-medium agar plate incubated at 37 °C for 24 h