FIGURE 5.

Mutants of ori γ sequences that impact ori α-mediated plasmid maintenance. A, diagram showing the normal and the mutated γ sequences. (+) means at least 500 colonies of IHF⁺ and/or ihfΔ cells carrying the plasmid derivatives plated on 40 μg/ml amp plates were recorded. (−) means that the ihfΔ host carrying the various plasmid derivatives formed less than 1% of the colonies formed by the IHF⁺ cells carrying the same plasmid derivative under identical conditions. Data are averages of three independent sets of experiments. The wt and the mutant form of the AT-rich region with the embedded ihf site are shown; the Xho1 insertion precisely separated the adjacent 7th iteron and the DnaA2 box. B, gel mobility shift experiments performed with 20 fmol of labeled ori γ probe/reaction and containing the wt or the mutated ihf site and incubated with the indicated amounts (fmol) of purified IHF. The mutant form of the ihf site failed to bind to the protein as contrasted with the normal ihf site.