FIG. 4.

Introduction of a Lac-Gent module by FLP recombination. A FRT site, which includes a 34-bp FRT core sequence, was introduced into the S. enterica serovar Typhimurium genome using the bacteriophage λ red recombination system (14, 74). Strains containing a single FRT site and the plasmid pCP20 (not shown), which contains a thermoinducible FLP recombinase, were induced for FLP expression and immediately transformed by electroporation with the 12-kb plasmid pPM1 (shown at bottom left). FLP recombination releases a 9.2-kb FRT-generated circle (bottom right) which can recombine into the chromosomal FRT site to generate a gentamicin-resistant strain with a lac operon flanked by res and FRT sites (top).