RFXAP Background Information The regulatory factor X (RFX) proteins include RFX1-5, RFX-B/Ank and RFX-associated protein (RFXAP). RFX proteins are essential class II transcription factors and activate the enhancer elements of several hepatitis B virus genes as well as promote the induction of MHC class II genes in response to interferon-g stimulation. Structural characteristics of the RFX family include a centrally located DNA-binding domain (DBD) and a C-terminal D region that facilitates dimerization. RFX5, RFX-B/Ank and RFXAP comprise the RFX trimer, which binds to X and S boxes in MHC class II promoters. Even though RFXAP lacks a DNA-binding domain, RFXAP and RFX-B/Ank are essential to the RFX DNA-binding function. The RFXAP interacts specifically with RFX5. Loss of RFXAP function is linked to MHC class II deficiency disease class D. The gene encoding human RFXAP maps to chromosome 13q13.3.
