MHC class II regulatory factor RFX has a novel DNA-binding domain and a functionally independent dimerization domain.

Abstract

The regulation of MHC class II gene expression controls T-cell activation and, hence, the immune response. Among the nuclear factors observed to bind to conserved DNA sequences in human leukocyte antigen (HLA) class II gene promoters, RFX is of special interest: Its binding is defective in congenital HLA class II deficiency, a disease of class II gene regulation. The cloning of an RFX cDNA has allowed us to show by transfection of a plasmid directing the synthesis of antisense RFX RNA that RFX is a class II gene regulatory factor. RFX is a novel 979-amino-acid DNA-binding protein that contains three structurally and functionally separate domains. The 91-amino-acid DNA-binding domain is distinct from other known DNA-binding motifs but may be distantly related to the helix-loop-helix motif. The most striking property of RFX is that it can bind stably to the class II X box as either a monomer or a homodimer and that the domain responsible for dimerization is distant from and functionally independent of the DNA-binding domain. This distinguishes RFX from other known dimeric DNA-binding proteins. It also implies that an RFX homodimer has two potential DNA-binding sites. We therefore speculate that RFX could form a DNA loop by cross-linking the two X-box sequences found far apart upstream of MHC class II genes.

Co-occupancy of the interferon regulatory element of the class II transactivator (CIITA) Type IV promoter by interferon regulatory factors 1 and 2

“…For full length IRF-1 and IRF-2, 200 ng IRF-1/pcDNA1 and IRF-2/ pcDNA1 plasmids, linearized by XhoI and XbaI, respectively, and transcribed in vitro by T7 RNA polymerase (Promega) as described (Reith et al, 1990). For C-terminal truncated IRF-2, termed IRF-2/T, IRF-2/pcDNA1 was linearized by BglII, which generated a C-terminal truncated IRF-2 cDNA fragment encompassing the 5' untranslated region and the coding sequence from amino acids 1 ± 224.…”

High mobility group I/Y protein functions as a specific cofactor for Oct-2A: mapping of interaction domains

“…In addition to a TATA motif, these include the X, Y, and Z boxes; elements whose sequences as well as stereospecific relationships to each other are highly conserved [16][17][18][19][20][21][22][23][24][25][26]. Several proteins that interact specifically with these cis-acting elements have been described [27][28][29][30][31][32][33][34][35][36][37][38]. A non-DNA binding protein (CIITA) whose expression pattern correlates with class II gene transcription and that strongly transactivates class II genes when expressed in class II-negative cells has also been identified [39,40].…”

YB-1 DNA-binding protein represses interferon gamma activation of class II major histocompatibility complex genes.

“…These two elements are separated by a 19-21-bp spacing that is conserved in length but not in sequence. The Y element contains an inverted CCAAT element, and the X element has been functionally divided into two subregions, X1 and X2, based on the separate interactions of these subregions with the RF-X and hXBP-1 recombinant DNA-binding proteins, respectively (10,11). The S sequence (also known as H, or W/Z which is a larger DNA sequence) is a heptamer sequence located upstream of the class II box (12)(13)(14)(15)(16)(17).…”