NORMAL GENOMIC

• Naamane H et al.
• The 752delG26 mutation in the RFXANK gene associated with majorhistocompatibility complex class II deficiency: evidence for a foundereffect in the Moroccan population.
• Eur J Pediatr. 2010; 169: 1069-74
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• Major histocompatibility complex class II plays a key role in the immuneresponse, by presenting processed antigens to CD4+ lymphocytes. Majorhistocompatibility complex class II expression is controlled at thetranscriptional level by at least four trans-acting genes: CIITA, RFXANK,RFX5 and RFXAP. Defects in these regulatory genes cause MHC class IIimmunodeficiency, which is frequent in North Africa. The aim of this studywas to describe the immunological and molecular characteristics of tenunrelated Moroccan patients with MHC class II deficiency. Immunologicalexaminations revealed a lack of expression of MHC class II molecules atthe surface of peripheral blood mononuclear cells, low CD4+ T lymphocytecounts and variable serum immunoglobulin (IgG, IgM and IgA) levels. Inaddition, no MHC class II (HLA DR) expression was observed onlymphoblasts. The molecular analysis identified the same homozygous752delG26 mutation in the RFXANK genes of all patients. This findingconfirms the association between the high frequency of the combinedimmunodeficiency and the defect in MHC class II expression and providesstrong evidence for a founder effect of the 752delG26 mutation in theNorth African population. These findings should facilitate theestablishment of molecular diagnosis and improve genetic counselling foraffected Moroccan families.

• Arimura Y, Tang WR, Koda T, Kakinuma M
• Structure of novel rat major histocompatibility complex class II genesRT1.Ha and Hb.
• Immunogenetics. 1995; 41: 320-5

• Steimle V, Siegrist CA, Mottet A, Lisowska-Grospierre B, Mach B
• Regulation of MHC class II expression by interferon-gamma mediated by thetransactivator gene CIITA.
• Science. 1994; 265: 106-9
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• Major histocompatibility complex (MHC) class II genes are expressedconstitutively in only a few cell types, but they can be induced in themajority of them, in particular by interferon-gamma (IFN-gamma). The MHCclass II transactivator gene CIITA is defective in a form of primary MHCclass II deficiency. Here it is shown that CIITA expression is controlledand induced by IFN-gamma. A functional CIITA gene is necessary for classII induction, and transfection of CIITA is sufficient to activateexpression of MHC class II genes in class II-negative cells in the absenceof IFN-gamma. CIITA is therefore a general regulator of both inducible andconstitutive MHC class II expression.

• Donald RG, Jackson AO
• The barley stripe mosaic virus gamma b gene encodes a multifunctionalcysteine-rich protein that affects pathogenesis.
• Plant Cell. 1994; 6: 1593-606
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• Barley stripe mosaic virus contains seven genes, one of which specifies a17-kD cysteine-rich protein, gamma b, that is known to affect virulence.To further characterize the role of gamma b in pathogenesis, wemutagenized sequences encoding amino acids within two clusters of cysteineand histidine residues in the cysteine-rich domain and a group of basicamino acids located between the clusters and determined the effects ofthese mutations on the symptom phenotype in barley. Three single aminoacid substitutions in cluster 1 and two amino acid exchanges in the basicregion caused bleached symptoms associated with pronounced elevations inaccumulation of gamma b protein. In contrast, three single amino acidsubstitutions in cluster 2 and a mutation in the basic motif resulted inattenuated ("null") symptoms typical of those produced when the gamma bgene is deleted. Tissue infected with these "null" mutants accumulatedslightly elevated amounts of the gamma b protein but significantly lowerlevels of coat protein and the putative movement protein beta b. Geneticcomplementation tests revealed that cluster 1 mutations are dominant overthe wild-type gamma b gene, whereas those in cluster 2 are recessive.These results highlight the pivotal role of gamma b in pathogenesis andsuggest that the two cysteine-rich clusters are functionally distinct andthat they affect different aspects of disease development.

• Riley JL, Boss JM
• Class II MHC transcriptional mutants are defective in higher order complexformation.
• J Immunol. 1993; 151: 6942-53
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• Human class II MHC genes are regulated in part by a series of conservedupstream sequence elements termed the X1, X2, and Y boxes. Class II MHCtranscriptional mutant B cell lines have been defined that differ withregard to the presence of RFX, an X1 box DNA-binding activity. To furthercharacterize these mutant cell lines, we tested the ability of theseconserved upstream elements to respond to the presence of knowntranscriptional activation domains. A series of HLA-DRA promoter reporterconstructions carrying Gal4 binding sites and GAL4 fusion proteinexpression vectors were cotransfected into both wild type B cells andmutant B cells representing the two RFX phenotypes. Regardless of RFX orclass II phenotype, the activation domains of GAL4-VP16 and GAL4-E1a couldsynergistically stimulate expression of constructions containing both theX2 and Y boxes. GAL4-VP16- and GAL4-E1a-mediated expression was inhibitedby the presence of the X1 box in cells that contained RFX. In mutant cellsthat lacked RFX, GAL4-VP16 activation was not inhibited. In theRFX-positive class II mutant cell line RJ2.2.5, the X1 box inhibitoryactivity could be overcome by separating the Gal4 site from the X1 box bytwo additional helical turns, suggesting that the RFX factor is bound atthe X1 site and sterically interferes with activation. This was not thecase in wild type B cells, suggesting that a stable higher order complexforms in wild type cells and not in the mutant cells.

• Seidl C, Saraiya C, Osterweil Z, Fu YP, Lee JS
• Genetic complexity of regulatory mutants defective for HLA class II geneexpression.
• J Immunol. 1992; 148: 1576-84
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• MHC (called HLA in man) class II genes play an essential role incell-mediated immunity. Absence of HLA class II Ag on B lymphocytes is thebasis of some congenital immunodeficiencies (CID). We have studied CID bygenerating transient heterokaryons from cell lines of such patients, andwe report that the mutations fall into four complementation groups. Inaddition, fusions with the HLA class II deletion mutant 721.180 indicatethat the genetic defects for each group in HLA class II expression mapoutside the HLA class II region. A small HLA-DRA promoter fragment issufficient to drive expression of a reporter gene in normal B cell lines,but expression from the same construct is clearly reduced in mutant celllines representative of all four complementation groups. This confirmsearlier results that indicate defective transcription of HLA class IIgenes in the class II- CID mutant cell lines. Analysis of proteins thatbind to the DRA promoter in nuclear extracts of the mutants suggests thatcomplexes recognizing distinct elements of the DRA promoter may bequantitatively decreased in different mutants. In addition, we show thatnuclear extracts from two groups fail to transcribe a DRA promoterconstruct in vitro accurately reflecting their DRA- phenotypes. Incontrast, nuclear extracts from another mutant, RJ2.2.5, transcribe theDRA construct, albeit at a reduced level. Finally, though cell lines fromdifferent groups complement each other in vivo, no complementation wasobserved by mixing extracts for transcription in vitro.

• Ono SJ, Liou HC, Davidon R, Strominger JL, Glimcher LH
• Human X-box-binding protein 1 is required for the transcription of asubset of human class II major histocompatibility genes and forms aheterodimer with c-fos.
• Proc Natl Acad Sci U S A. 1991; 88: 4309-12
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• A complementary DNA encoding a member of the leucine-zipper class ofproteins (human X-box-binding protein, hXBP-1) that binds to the 3' end ofthe conserved X box (X2) of the HLA-DRA major histocompatibility complexgene was recently described. Further gel-retardation analysis hasdemonstrated that hXBP-1 also binds to HLA-DPB X2 but not to other X2sequences. Transient transfection of a mammalian expression vector withthe hXBP-1 cDNA inserted in the antisense orientation represses thesurface expression of HLA-DR and HLA-DP in Raji cells. Cotransfection ofthe antisense hXBP-1 vector with a HLA-DRA/chloramphenicolacetyltransferase (but not a HLA-DQB/chloramphenicol acetyltransferase)reporter plasmid decreases chloramphenicol acetyltransferase activity inRaji cells and in gamma-interferon-treated HeLa cells relative to cellscotransfected with a control antisense vector. Moreover, hXBP-1 is shownto form a stable heterodimer with the product of the c-fos protooncogene.These data suggest that the hXBP-1 c-fos heterodimer is critical for thetranscription of a subset of the human class II major histocompatibilitycomplex genes and that the regulatory mechanisms for the different classII genes are distinct.

• Zoorob R, Behar G, Kroemer G, Auffray C
• Organization of a functional chicken class II B gene.
• Immunogenetics. 1990; 31: 179-87
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• Five class II (B-L) B genes are encoded in the major histocompatibilitycomplex (MHC) of chickens of the B12 haplotype. We report here thenucleotide sequence of one of these genes, B-LBII, as well as the primarystructure of a corresponding cDNA. The organization of B-LBII, its 5'flanking region including the promotor region, and the amino acid sequenceof its product are compared to mammalian class II B genes and to thepreviously described B-LBIII gene, which probably is a pseudogene since noB-LBIII transcript could be identified. The 5' flanking region of B-LBIIexhibits homologs of transcription-controlling sequence motifs, namely S,X, X2, and Y boxes, of class II A and B genes of rodents and man. However,the promotor region of B-LBIII lacks an equivalent of the S box, displaystwo nucleic acid substitutions in the core sequence of the Y box, andexhibits a 16 base pair (bp) deletion upstream of the site of initiationof transcription. Therefore, an aberrant promotor region is likely toaccount for the pseudogene-like nature of B-LBIII, which displaysopen-reading frames in all exons. The data obtained with the functionalB-LBII gene are in line with our previous interpretation that both genomicorganization and tertiary structure of class II beta molecules areremarkably conserved between birds and mammals.

• Freyd G, Kim SK, Horvitz HR
• Novel cysteine-rich motif and homeodomain in the product of theCaenorhabditis elegans cell lineage gene lin-11.
• Nature. 1990; 344: 876-9
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• The gene lin-11 is required for the asymmetric division of a vulvalprecursor cell type in the nematode Caenorhabditis elegans. Putativelin-11 complementary DNAs were sequenced and found to encode a proteinthat contains both a homeodomain and two tandem copies of a novelcysteine-rich motif: C-X2-C-X17-19-H-X2-C-X2-C-X2-C-X7-11-(C)-X8-C. Twotandem copies of this motif are also present amino-terminal to thehomeodomains in the proteins encoded by the genes mec-3, which is requiredfor C. elegans touch neuron differentiation, and isl-1, which encodes arat insulin I gene enhancer-binding protein. The arrangement of cysteineresidues in this motif, referred to as LIM (for lin-11 isl-1 mec-3),suggests that this region is a metal-binding domain. The presence in thesethree proteins of both a potential metal-binding domain and a homeodomaindistinguishes them from previously characterized proteins.

• Tsang SY, Nakanishi M, Peterlin BM
• Mutational analysis of the DRA promoter: cis-acting sequences andtrans-acting factors.
• Mol Cell Biol. 1990; 10: 711-9
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• Class II major histocompatibility genes are expressed at high levels in Blymphocytes and are gamma interferon (IFN-gamma) inducible in many othercells. Previously, we observed that DRA promoter sequences from positions-150 to +31 determine the tissue specificity of this class II gene.Moreover, Z and X boxes located between positions -145 and -87 conferredB-cell specificity and IFN-gamma inducibility upon a heterologouspromoter. In this study, sequences from positions -145 to -35 in the DRApromoter were systematically mutated by using oligonucleotide cassettes. Z(-131 to -125), pyrimidine (-116 to -109), X (-108 to -95), Y (-73 to-61), and octamer (-52 to -45) boxes were required for B-cell specificityand, with the exception of the octamer box, for IFN-gamma inducibility. Zbox and sequences flanking Z and X boxes helped to determine low levels ofexpression in T and uninduced cells. In phenotypically distinct cells,shared and distinct proteins bound to these conserved upstream sequences.However, few correlations between expression and DNA-binding proteinscould be made. Similar proteins bound to Z and X boxes, and the Z box mostlikely represents a duplication of the X box.

• Sikorska EJ
• [Formation of immunoglobulins].
• Postepy Hig Med Dosw. 1984; 38: 427-49

• Kawakami M
• [Genetics of immunoresponse (author's transl)].
• Jikken Dobutsu. 1981; 30: 47-58