Structural details of the human cytochrome P-450c gene

Aryl hydrocarbon hydroxylase activity is most closely associated with cytochrome P-450c in the rat and cytochrome P1-450 in the mouse. The sequence for the orthologous human gene coding for this enzymatic activity has been determined from several sources: cytochrome P-450c isolated from human embryonic DNA [K. Kawajiri, J. Watanabe, O. Gotoh, Y. Tagashiri, K. Sogawa, and Y. Fujii-Kuriyama (1986) Eur. J. Biochem. 139, 219-225], human lymphocytes in our own laboratory, and cytochrome P1-450 isolated from the established human breast carcinoma cell line, MCF-7 [A.K. Jaiswal, F. J. Gonzalez, and D. W. Nebert (1985) Nucleic Acids Res. 13, 4503-4520]. The data from our laboratory agree well with the sequence derived from human embryonic DNA, but differs significantly from that reported for the gene isolated from MCF-7 cells. Among these differences are a 320-bp insert and a 650-bp deletion in intron 1 relative to the sequence derived from the established cell line. We observe two mRNA species that hybridize to cytochrome P-450c probes, one expected at 2.7 kb and an additional 2.0-kb species. Finally, we note additional hybridization bands in 11% of the population examined by Southern blot analysis, representing either a second rare allele or, more likely, a duplication of at least a portion of the cytochrome P-450c gene.