RFXANK, along with regulatory factor X-associated protein and regulatory factor-5, forms a complex that binds to the X box motif of certain MHC class II gene promoters and activates their transcription. Once bound to the promoter, this complex associates with the non-DNA-binding factor MHC class II transactivator, which controls the cell type specificity and inducibility of MHC class II gene expression. This protein contains ankyrin repeats involved in protein-protein interactions. Mutations in this gene have been linked to bare lymphocyte syndrome type II, complementation group B. Two transcript variants encoding different isoforms have been described for this gene, with only one isoform showing activation activity. Recombinant human RFXANK protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.