This is the N-terminal domain of regulatory factor X (RFX)-5 protein of the RFX complex present in Homo sapiens. The RFX complex is made up of RFX5, RFXAP and RFXB. The complex is involved in the regulation of the expression of the major histocompatibility complex class II (MHCII) gene products. These gene products are essential for the initiation and regulation of the mammalian immune response. The N-terminal domain of RFX5 is responsible for homodimerization of RFX5 which promotes folding of the C-terminal domain of RFXAP. The folding of RFXAP results in the formation of a potential binding site for RFXB to bind to the MHCII promoter [1].

1: Solution structure of the heterotrimeric complex between the interaction domains of RFX5 and RFXAP from the RFX gene regulatory complex. Laird KM, Briggs LL, Boss JM, Summers MF, Garvie CW; J Mol Biol. 2010;403:40-51. PMID:20732328