Sakurai M, Strominger J L
Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, MA 02138.
Proc Natl Acad Sci U S A. 1988 Sep;85(18):6909-13. doi: 10.1073/pnas.85.18.6909.
A 95-base-pair immediate upstream sequence of the human class II major histocompatibility complex DQB gene containing the conserved X and Y elements showed enhancer activity in a transient expression assay. An "enhancer test plasmid" harboring the bacterial chloramphenicol acetyltransferase gene under the control of a truncated simian virus 40 enhancerless early promoter was employed. The DQB sequence inserted into this plasmid was active as an enhancer in Raji cells (human Burkitt lymphoma cells) but not active in Jurkat cells (human T-cell leukemia cells) or in HeLa cells (human cervical carcinoma cells). This cell-type specificity suggests that this enhancer activity may be involved in the tissue specificity of the DQB gene that is normally expressed only in mature B cells, macrophages, and thymic epithelial cells. Deletion analysis showed that both X and Y box sequences are essential for the full activity of the enhancer sequence and that these two sequences may function in a cooperative manner as cis-acting elements. Further deletions were used to define the 5' border of the X element. These results suggest that previously characterized protein factors that bind to X and Y include transcription factors involved in the cell-type specificity of this enhancer activity.
包含保守的X和Y元件的人类II类主要组织相容性复合体DQB基因的一段95个碱基对的紧邻上游序列，在瞬时表达试验中显示出增强子活性。使用了一种“增强子测试质粒”，该质粒在截短的猿猴病毒40无增强子早期启动子的控制下携带细菌氯霉素乙酰转移酶基因。插入该质粒的DQB序列在Raji细胞（人伯基特淋巴瘤细胞）中作为增强子具有活性，但在Jurkat细胞（人T细胞白血病细胞）或HeLa细胞（人子宫颈癌细胞）中无活性。这种细胞类型特异性表明，这种增强子活性可能与DQB基因的组织特异性有关，DQB基因通常仅在成熟B细胞、巨噬细胞和胸腺上皮细胞中表达。缺失分析表明，X和Y框序列对于增强子序列的完全活性都是必需 的，并且这两个序列可能作为顺式作用元件以协同方式发挥作用。进一步的缺失用于确定X元件的5'边界。这些结果表明，先前鉴定的与X和Y结合的蛋白质因子包括参与这种增强子活性的细胞类型特异性的转录因子。
