In vitro interactions of integration host factor with the ompF promoter-regulatory region of Escherichia coli.

Previous work has shown that integration host factor (IHF) mutants have increased expression and altered osmoregulation of OmpF, a major Escherichia coli outer membrane protein. By in vitro analysis the possibility was investigated that IHF interacts directly with the ompF promoter region. Gel retardation assays and DNase I protection experiments showed that IHF binds to two sites in the ompF promoter region centered at positions -180 and -60 relative to the start of transcription. Gel electrophoresis studies with circularly permuted ompF promoter fragments indicated that IHF binding strongly increased a small intrinsic bend in the ompF promoter region. The addition of IHF to a purified in vitro transcription system strongly and specifically inhibited ompF transcription. This inhibition was reversed by increasing the concentration of OmpR, a positive activator required for ompF expression, suggesting that IHF may inhibit ompF transcription by altering how OmpR interacts with the ompF promoter.