Analysis of Dioxin Responsive Elements (DREs) in Drug-inducible Eel CYP1A Gene

Abstract

Exposure of animals to dioxin or similar environmental pollutants evokes responses by some drug-inducible genes that are measurable in the transcriptional level for using in the early detection system. Dioxin responsive elements (DREs) located in the 5' upstream regions of the CYP1A genes of fish and other animals play a key role in the drug-inducible genes expression. Of the two CYP1A genes reported in Japanese eel, several DREs are found to exist in the 5' upstream region of the CYP1A1 (MC1) gene. However, no DREs was found within the 1631 bp upstream region of the second form of CYP1A1 (MC2) gene in a λ phage clone. In order to sequence further beyond the 1.6 kbp upstream region of the MC2 gene, a cosmid library was constructed with longer genomic fragments. We succeeded in obtaining a clone which contained both the MC1 and the MC2 genes including the further upstream region of the MC2 gene. Sequence analysis revealed that the clone contained, in addition to the 1.6 kbp region, a 3295 bp further upstream region containing eleven DREs. In MC1 as well as mammalian CYP1A1 genes, the functional DREs are found in the proximity of transcription start site, whereas the DREs of the MC2 gene were localized beyond the 1.7 kbp upstream region, which contains unusual TAA repeats.