Xenobiotic microsomal epoxide hydrolase: 5' sequence of the human gene

A cDNA for human microsomal epoxide hydrolase (mEH) was used to isolate genomic clones representing the 5' portion of the corresponding human gene. A total of 1034 bases of mEH gene sequence were obtained that included exon 1 and 5' flanking information. In contrast to the structure reported for the rat mEH gene (Falany et al. (1987) J. Biol. Chem. 262, 5924-5930), the human mEH gene lacked a CAAT box, but did contain a high-affinity CTF binding site at position -278 and an SV40 core enhancer element at position -525. TATA boxes were identified at positions -32 and -29 for the human and rat genes, respectively. Sequence comparisons between 5' flanking regions of the human and rat mEH genes demonstrated 47% homology, considerably less than the 83% conservation observed in the cDNA coding areas. Primer extension experiments localized the transcription initiation site of the human gene to a position 116 bases 5' from the analogous site in the rat mEH gene.