Site-specific DNA binding and bending by the Borrelia burgdorferi Hbb protein

The Borrelia burgdorferi Hbb protein shows sequence similarity to members o f the Escherichia coli HU/integration host factor (IHF) family of DNA acces sory factors. We have overexpressed the hbb gene product in E. coli and pur ified the protein to near homogeneity. Biochemical analyses have revealed t hat Hbb has unique properties and is neither a strict HU nor IHF analogue. Hbb was found to bind specifically to a site in the putative origin of DNA replication between dnaA and dnaN. DNA footprinting studies have shown that this site is unrelated to the consensus sequence recognized by IHF protein s. Hbb induces a dramatic bend (> 126 degrees) at this site and was also sh own to restrain negative supercoils efficiently upon DNA binding. These fea tures of the protein suggest that Hbb may act as a DNA accessory factor tha t facilitates the assembly of higher order protein-DNA complexes, such as t hose involved in DNA replication, transcription, recombination, packaging a nd perhaps other DNA metabolic processes unique to Borrelia.