FIG 3.

Allelic switching demonstrates that ripA and ripB are individually dispensable but that at least one of the two enzymes is required for viability. (A) Schematic diagram of the native ripAB locus and the attL5 site for the various allelic switching strategies. (B) Photographs of agar plates of allelic switching transformations to replace the streptomycin resistance ripAB plasmid at the attL5 locus with kanamycin resistance plasmids expressing both ripA and ripB (ΔripAB::ripAB), ripA (ΔripAB::ripA) or ripB (ΔripAB::ripB) alone, or an empty plasmid (pTC-MCS).