Replacement of integration host factor protein-induced DNA bending by flexible regions of DNA

The Escherichia coli integration host factor (IHF) protein is required for site-specific recombination of bacteriophage A DNA. Previously, we had show n that alternative modules of static DNA curvature could partially replace IHF in recombination. Now we use regions of single-stranded DNA as a flexib le tether to address whether the function of IHF in recombination is simply to reduce persistence length. Although we find that these modules clearly enhance recombination in the absence of IHF, they are not perfect replaceme nts. In addition, evidence is presented that the efficacy of a flexibility swap is specific to a particular IHF site. This may indicate that additiona l functions beyond simple deformation of DNA are required of IHF. During th e course of these experiments we discovered that these flexible sequences a re still specific sites for IHF binding and function.