Bacterially produced human HIF-1α is competent for heterodimerization and specific DNA-binding

Hypoxia-inducible factor 1α (HIF-1α) is the regulatory subunit of HIF-1, the transcriptional activator and key mediator of the cellular response to hypoxia. Regulation of HIF-1α occurs at multiple levels and involves several different post-translational modifications. In order to examine the importance of these modifications for the basic function of HIF-1α, we have produced in bacteria recombinant full-length human HIF-1α using different expression systems. We show that this unmodified form of HIF-1α is able to form a stable heterodimer with the second subunit of HIF-1 (HIF-1β or ARNT) when both proteins are co-expressed in Escherichia coli. Furthermore, this bacterially reconstituted heterodimer exhibits specific DNA-binding activity. These data indicate that post-translational modification of HIF-1α is not essential for its interaction with ARNT and DNA, and provide an in vitro system for the characterization of the molecular properties of HIF-1α.