Hassett C, Robinson K B, Beck N B, Omiecinski C J
Department of Environmental Health, School of Public Health and Community Medicine, University of Washington, Seattle 98195.
Genomics. 1994 Sep 15;23(2):433-42. doi: 10.1006/geno.1994.1520.
Human microsomal epoxide hydrolase (mEH) is a xenobiotic-metabolizing enzyme that detoxifies reactive epoxides to more water soluble dihydrodiol compounds. We have isolated and sequenced clones that encode the entire human mEH gene (EPHX1). The primary nuclear transcript, extending from the start of transcription to the site of poly(A) addition, is 20,271 nucleotides in length. The human mEH gene contains 9 exons, separated by 8 introns; canonical intron/exon boundary sites are observed at each junction. The introns vary in size from 335 to 6696 bp and contain numerous repetitive DNA elements, including 18 Alu sequences (each > 100 nucleotides in length) within 4 introns. Alu sequences were classified with respect to subfamily assignment. Two thousand eighteen nucleotides 5' of the transcription start and 2501 nucleotides 3' of the poly(A) addition sites were also sequenced. To evaluate the human mEH promoter, chimeric constructs were prepared linking portions of the 5' mEH flanking sequence (up to -693 bp) to a CAT reporter gene, followed by transient transfection in both COS-1. and HepG2 cells. Results from these expression experiments suggest that the human mEH gene contains a weak core promoter and that inclusion of DNA sequences 5' of the minimal promoter region negatively regulates constitutive transcription.
人微粒体环氧化物水解酶（mEH）是一种外源性物质代谢酶，可将反应性环氧化物解毒为水溶性更高的二氢二醇化合物。我们已经分离并测序了编码整个人mEH基因（EPHX1）的克隆。从转录起始到聚腺苷酸化位点的初级核转录本长度为20271个核苷酸。人mEH基因包含9个外显子，由8个内含子隔开；在每个连接处均观察到典型的内含子/外显子边界位点。内含子大小从335到6696 bp不等，包含许多重复DNA元件，包括4个内含子中的18个Alu序列（每个长度> 100个核苷酸）。根据亚家族分配对Alu序列进行了分类。还对转录起始点上游2018个核苷酸和聚腺苷酸化位点下游2501个核苷酸进行了测序。为了评估人mEH启动子，制备了嵌合构建体，将5'mEH侧翼序列的部分（至-693 bp）与CAT报告基因连接，然后在COS-1和HepG2细胞中进行瞬时转染。这些表达实验的结果表明，人mEH基因包含一个弱核心启动子，并且最小启动子区域上游的DNA序列的包含对组成型转录具有负调控作用。
