FIG. 2.

Genotypic characterization of invertible element orientation in phase-locked mutants. E. coli CFT073 and its isogenic phase-locked mutants were cultured for 18 h statically in Luria broth and used directly for PCR (A) or transurethrally inoculated independently into mice, whose urine collected at 72 hpi was used for PCR (B). The invertible element amplified by PCR was digested with SnaBI; following both in vitro and in vivo growth, asymmetric cutting demonstrates that the orientation of the invertible element in the parent strain CFT073 is both in the on and off position. CFT073^OFF remains only in the off orientation; CFT073^ON remains only in the on orientation.