An eel cytochrome P450 1A gene having no XRE sequences in its 5 ' upstreamregion of 1600 bp

The gene family cytochrome P450 (CYP) 1A is ubiquitous among animals, and C YP1A1 genes have been identified in teleost and mammals. We isolated anothe r CYP1A gene, which is inducibly expressed by exposure to 3-methylcholanthr ene, from the genomic library of the eel (Anguilla japonica). The genomic d one obtained, approximately 17,500 bp in length, contained the structural g ene of the CYP1A and a 5' upstream region of about 1600 bp. Sequence analys is of the 5' upstream region and the first and second exons revealed that t he 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 upstr eam from the transcriptional start site, respectively. Unlike the CYP1A1 ge nes of eel and other animals, we found no xenobiotic responsive element (XR E) core sequences in the 5' upstream region studied (1631 bp) or in the fir st intron, whereas three peculiar regions, each composed of multiple repeat s of the trinucleotide TAA, were found between 824 and 1356 bp upstream fro m the transcriptional start site. Absence of XRE core sequences and presenc e of the multiple repeats in the 51 upstream region sequenced may suggest t hat the expression mechanism of the eel CYP1A gene is somewhat different fr om the mechanisms of other reported CYP1A genes.