Expression and purification of human FANCI and FANCD2 using Escherichia coli cells

•Human FANCI and FANCD2 proteins were overexpressed and purified using E. coli cells.•Bacterially produced human FANCI and FANCD2 formed the ID heterodimer.•The purified human ID complex preferentially bound to branched DNA structures.•The purified human ID complex possessed histone chaperone activity. The DNA interstrand crosslink (ICL) is an extremely deleterious DNA lesion that covalently crosslinks complementary strands and prevents the strand-separation reaction. In higher eukaryotes, the Fanconi anemia proteins, FANCI and FANCD2, form a heterodimer and play essential roles in ICL repair. Human FANCI and FANCD2 are large proteins with molecular masses of 149kDa and 164kDa, respectively, and were reportedly purified using a baculovirus expression system with insect cells. We have established a novel expression and purification procedure for human FANCD2 and FANCI, using Escherichia coli cells. The human FANCD2 and FANCI proteins purified by this bacterial expression method formed a stable heterodimer, and exhibited DNA binding and histone chaperone activities, as previously reported for the proteins purified by the baculovirus system. Therefore, these purification methods for human FANCI and FANCD2 provide novel procedures to facilitate structural and biochemical studies of human FANCI and FANCD2.