Human class II MHC Ag are a family of cell surface glycoproteins. Their constitutive expression is limited to B lymphocytes and thymic epithelial cells. In many other cells their expression can be induced by IFN-gamma. Conserved upstream promoter sequences regulate this tissue-specific expression of class II genes. In the DRA promoter, one of these cis-acting regulatory motifs is the X2-box to which nuclear factor X2 (NF-X2) binds. Here, we present the isolation and characterization of the full-length cDNA clone encoding NF-X2. This cDNA clone was isolated by expression cDNA cloning, and encodes the human c-Jun protein, which together with c-Fos forms the heterodimeric activator protein-1 transcription complex. Whereas c-Fos/c-Jun heterodimers do not exist in B cells, they form and bind to the X2-box in class II nonexpressing cells. Thus, c-Fos/c-Jun heterodimers might contribute to the repression of DRA gene expression.

译文

人类II类MHC Ag是细胞表面糖蛋白家族。它们的组成型表达仅限于B淋巴细胞和胸腺上皮细胞。在许多其他细胞中,它们的表达可以通过IFN-γ 诱导。保守的上游启动子序列调节II类基因的这种组织特异性表达。在DRA启动子中,这些顺式作用调节基序之一是核因子X2 (NF-X2) 结合的X2-box。在这里,我们介绍了编码NF-X2的全长cDNA克隆隔离和表征。通过表达cDNA克隆分离该cDNA克隆,并编码人c 6月蛋白,该蛋白与c-Fos一起形成异二聚体激活蛋白1转录复合物。尽管b细胞中不存在c-Fos/c-6月异二聚体,但它们在II类非表达细胞中形成并结合X2-box。因此,c-Fos/c-6月异二聚体可能有助于抑制DRA基因表达。

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