FIG. 3.

(A) Allelic exchange strategy. The vacA gene of wild-type strain G27 (a) is replaced by a double crossover event with that of construct Pr (b) to generate the recipitent strain G27::Pr, resulting in resistance to kanamycin. Allelic exchange between the Pr sequences and those of the delivery constructs (c) containing the chimeric genes results in resistance to chloramphenicol and sensitivity to kanamycin. The antibiotic resistance phenotypes of the resulting strains are shown at the right. (B) Schematic representation of the constructed chimeras. The shaded box shows replacement of m1 vacA sequence by m2 sequences. Amino acid positions starting from the initiation codon of the vacA gene (strain 11638) are shown.