Purification of the integration host factor homolog of Rhodobacter capsulatus: cloning and sequencing of the hip gene, which encodes the beta subunit.

We describe a method for rapid purification of the integration host factor (IHF) homolog of Rhodobacter capsulatus that has allowed us to obtain microgram quantities of highly purified protein. R. capsulatus IHF is an alpha beta heterodimer similar to IHF of Escherichia coli. We have cloned and sequenced the hip gene, which encodes the beta subunit. The deduced amino acid sequence (10.7 kDa) has 46% identity with the beta subunit of IHF from E. coli. In gel electrophoretic mobility shift DNA binding assays, R. capsulatus IHF was able to form a stable complex in a site-specific manner with a DNA fragment isolated from the promoter of the structural hupSL operon, which contains the IHF-binding site. The mutated IHF protein isolated from the Hup- mutant IR4, which is mutated in the himA gene (coding for the alpha subunit), gave a shifted band of greater mobility, and DNase I footprinting analysis has shown that the mutated IHF interacts with the DNA fragment from the hupSL promoter region differently from the way that the wild-type IHF does.