Evaluation of the effect of mutations in the proposed IHF binding site. Gel mobility shift assays using the mutant probes of fragment I (104 bp). Panel A shows the assays using mutant probe 1, which contains changes in the dA-dT rich upstream region as well as changes of C to A and G to T in the consensus sequence. These changes caused a decrease of 89% with respect to the control. Panel B shows assays using mutant probe 2, which also includes mutations in the TTR region of the consensus sequence, causing an 86% decrease in the retarded signal. The asterisks indicate the bases modified. The bold red letters indicate the proposed site for IHF binding.