FIG. 2.

Inversion of the fimS element by FimB and its mutant derivatives. Inversion of fimS was detected by a PCR assay. The structures of the phase-on and phase-off substrates are summarized at the top, together with details of the oligonucleotide primers used to amplify the inversion products. Gels with the PCR products obtained with phase-on and phase-off substrates are shown below. The positions to which PCR products diagnostic of phase-on or phase-off switches migrate are indicated to the right of each gel. Inversion of fimS is seen only in the case of the wild-type FimB protein (third lane from the left). DNA size markers are shown in the first lane; pUC18 is the vector-only control.