Integration host factor alters LacI-induced DNA looping.

The integration host factor protein of Escherichia coli, which sharply bends DNA at specific sites and non-specifically compacts the bacterial genome, can also alter looping of DNA in an artificial system based on the lactose repressor protein of E. coli. In single molecule experiments, we show that both specific bending and non-specific compaction alter LacI-mediated looping of DNA. Our results highlight the subtle regulatory roles that proteins, which confer structure upon DNA, might have in controlling DNA transcription and other processes in which the conformation of DNA determines the binding and activity of processive enzymes.