Dependency of glpFK promoter activation on IHF binding to IB (A–C) as well as the A-tract-promoting permanent bend in IB (D).

(A) Growth of crp Glp⁺ (•), ihfA (σ) and crp Glp⁺ihfA (▒) cells in liquid glycerol (1%) M9 minimal medium. (B) Effect of a host ihfA null mutation on IB:PglpFK activity. (C) Effect of IHF binding site mutations in IB on IB:PglpFK activity. ‘None’, ‘single’, and ‘double’ refer to no mutation, mutation of TCAA (−221 to −218 relative to +1 of PglpFK) to GTCT, and mutation of TCAA to GTCT as well as TT (−213 to −212) to GC in the IHF binding site located in IB, respectively (see Figure 1B). (D) lacZ expression measured by β-galactosidase assay for crp cells carrying an IB:PglpFK-lacZ fusion with various A-tract mutations in IB. The strain bearing altered A-tracts 4–8 includes the mutations shown in A-tracts 4–8. ‘none’, ‘A-tracts 4–8’, ‘A-tract 3’ and ‘A-tracts 1–3’ refer to no mutation, mutations in A-tracts 4 to 8, mutation in A-tract 3 and mutations in A-tracts 1 to 3, respectively (see Figure 1B).