The rat P450IIE1 gene: complete intron and exon sequence, chromosome mapping, and correlation of developmental expression with specific 5' cytosine demethylation.

The gene coding for the ethanol-inducible, developmentally regulated P450IIE1 was isolated from an lambda EMBL 3 rat genomic library and completely sequenced. The gene spanned 10,373 base pairs and contained nine exons. Upstream and downstream DNA of 1530 and 825 base pairs, respectively, was also sequenced, and the transcription start site was identified by both S1 mapping and primer extension. A typical TATA box was found just upstream of the start site; however, no CCAAT box was apparent. Other repetitive sequences were identified including a partial R.dre.1 sequence upstream of the gene and a long stretch of 160 alternating purines in the second intron. This latter repetitive element is found in many mammalian genes. By use of a panel of mouse-hamster somatic cell hybrids, the P450IIE1 gene was localized to mouse chromosome 7. The hepatic P450IIE1 gene is transcriptionally activated within 1 day after birth and reaches a maximal level of expression at 6 days of age. Using restriction endonuclease sites generated from the gene sequence data and the cytosine methylation-sensitive enzymes HhaI and HpaII, we found that this transcriptional activation during early development is coincident with specific demethylation only at the 5' end of the P450IIE1 gene. Interestingly, other cytosine residues in the middle of the gene became demethylated as rats aged from 1 to 10 weeks, at which time no changes in gene expression occur.