This C-terminal domain of Regulatory factor X-associated protein binds to RFXANK [1,2], the Ankyrin-repeat regulatory factor X proteins. RFXA is part of the RFX complex, Mutants of either RFXAP or RFXANK protein fail to bind to each other. RFX5 binds only to the RFXANK-RFXAP scaffold and not to either protein alone, and neither the scaffold nor RFX5 alone can bind DNA. The binding of the RFXANK-RFXAP scaffold to RFX5 leads to a conformational change in the latter that exposes the DNA-binding domain of RFX5. The DNA-binding domain of RFX5 anchors the RFX complex to MHC class II X and S promoter boxes [3].

1: RFXAP, a novel subunit of the RFX DNA binding complex is mutated in MHC class II deficiency. Durand B, Sperisen P, Emery P, Barras E, Zufferey M, Mach B, Reith W; EMBO J. 1997;16:1045-1055. PMID:9118943

2: RFX-B is the gene responsible for the most common cause of the bare lymphocyte syndrome, an MHC class II immunodeficiency. Nagarajan UM, Louis-Plence P, DeSandro A, Nilsen R, Bushey A, Boss JM; Immunity. 1999;10:153-162. PMID:10072068

3: Mutations in the bare lymphocyte syndrome define critical steps in the assembly of the regulatory factor X complex. Nekrep N, Jabrane-Ferrat N, Peterlin BM; Mol Cell Biol. 2000;20:4455-4461. PMID:10825209