Gel shift assays using Escherichia coli mutant strains and purified IHF protein. Gel shift assays were performed as described in Methods. (A) Protein extracts of E. coli mutants for subunits of HU (hupA, hupB) and IHF proteins (ihfA and ihfB) were used in these assays. The arrow indicates the DNA-protein complex formed. (B) Gel shift assay using the purified IHF protein from E. coli (IHFr), which produces a retarded signal similar to that obtained with the extract of P. syringae pv. phaseolicola. The probe used in this assay corresponds to the 104 bp region. The band shifted is indicated by an arrow.