An Eel Cytochrome P450 1A Gene Having No XRE Sequences in Its 5′ Upstream Region of 1600 bp

The gene family cytochrome P450 (CYP) 1A is ubiquitous among animals, and CYP1A1 genes have been identified in teleost and mammals. We isolated another CYP1A gene, which is inducibly expressed by exposure to 3-methylcholanthrene, from the genomic library of the eel (Anguilla japonica). The genomic clone obtained, approximately 17,500 bp in length, contained the structural gene of the CYP1A and a 5′ upstream region of about 1600 bp. Sequence analysis of the 5′ upstream region and the first and second exons revealed that the initiation codon was in the second exon, as in the CYP1A genes reported for mammals and teleosts. CAAT and TATA boxes were found 51 and 29 bp upstream from the transcriptional start site, respectively. Unlike the CYP1A1 genes of eel and other animals, we found no xenobiotic responsive element (XRE) core sequences in the 5′ upstream region studied (1631 bp) or in the first intron, whereas three peculiar regions, each composed of multiple repeats of the trinucleotide TAA, were found between 824 and 1356 bp upstream from the transcriptional start site. Absence of XRE core sequences and presence of the multiple repeats in the 5′ upstream region sequenced may suggest that the expression mechanism of the eel CYP1A gene is somewhat different from the mechanisms of other reported CYP1A genes.