A gene encoding a novel RFX-associated transactivator is mutated in the majority of MHC class II deficiency patients.
Major histocompatibility class II (MHC-II) molecules are transmembrane proteins that have a central role in development and control of the immune system. They are encoded by a multigene family and their expression is tightly regulated. MHC-II deficiency (OMIM 209920) is an autosomal recessive immunodeficiency syndrome resulting from defects in trans-acting factors essential for transcription of MHC-II genes. There are four genetic complementation groups (A, B, C and D), reflecting the existence of four MHC-II regulators. The factors defective in groups A (CIITA), C (RFX5) and D (RFXAP) have been identified. CIITA is a non-DNA-binding co-activator that controls the cell-type specificity and inducibility of MHC-II expression. RFX5 and RFXAP are two subunits of RFX, a multi-protein complex that binds the X box motif of MHC-II promoters. Mutations in the genes encoding RFX5 (RFX5) or RFXAP (RFXAP) abolish binding of RFX (refs 7,8,12). Similar to groups C and D, group B is characterized by a defect in RFX binding, and although it accounts for the majority of patients, the factor defective in group B has remained unknown. We report here the isolation of RFX by a novel single-step DNA-affinity purification approach and the identification of RFXANK, the gene encoding a third subunit of RFX. RFXANK restores MHC-II expression in cell lines from patients in group B and is mutated in these patients. RFXANK contains a protein-protein interaction region consisting of three ankyrin repeats. Its interaction with RFX5 and RFXAP is essential for binding of the RFX complex to MHC-II promoters.
Masternak
K
K
Louis Jeantet Laboratory of Molecular Genetics, Department of Genetics and Microbiology, University of Geneva Medical School, Switzerland.
Barras
E
E
Zufferey
M
M
Conrad
B
B
Corthals
G
G
Aebersold
R
R
Sanchez
J C
JC
Hochstrasser
D F
DF
Mach
B
B
Reith
W
W
D000595:Amino Acid Sequence; D001483:Base Sequence; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005802:Genes, MHC Class II; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D006801:Humans; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree; D011401:Promoter Regions, Genetic; D000071701:Regulatory Factor X Transcription Factors; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism
D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D000949:Histocompatibility Antigens Class II; D000071701:Regulatory Factor X Transcription Factors; D015534:Trans-Activators; D014157:Transcription Factors