Structures and characterization of sex‐specific mouse cytochrome P‐450 genes as members within a large family

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Abstract
We characterized two female‐specific testosterone 16α‐hydroxylase mouse cytochrome P‐450 genes, 16αoh‐a and 16αoh‐b. Gene 16αoh‐a, consisting of nine exons, is approximately 38 kbp in size. The exon sequence of this P‐450 gene is identical to cDNA pf26 nucleotide sequence [Noshiro, M., Lakso, M., Kawajiri, K. & Negishi, M. (1988) Biochemistry 27, 6434–6443], which encodes female‐specific testosterone 16α‐hydroxylase regulated by the murine Rip locus. Gene 16αoh‐b, containing nine exons with the same junctions as the 16αoh‐a, spans at least 20 kbp, and encodes a cytochrome P‐450 whose deduced amino acid sequence is 90% similar to the hydroxylase. Nucleotide sequences revealed that duplication of the two genes occurred 4–22 million years ago, and that the 5′ duplication boundary is located 1336 bp upstream from the putative transcription‐start site. In the flanking regions of both genes, there is a long stretch (100 bp) of CA repeats in addition to other motifs, including TATA box, glucocorticoid‐response‐element‐core and Simian‐virus‐40‐enhancer sequences and IgG light‐chain gene promoter. We isolated many genomic DNA clones which contain exon 1 sequences, and compared their restriction maps, cross‐hybridization and nucleotide sequences. The results indicate that these genomic clones represent closely related genes in the 16αoh family with a minimum of 16 members, which is further divided into classes a, b and c. 16αoh‐a and 16αoh‐b belong to the first and second classes, respectively. Moreover, extensive segmental gene conversion and nonreciprocal recombination were noted among the genes, particularly among those in class b. All genes in that class contain the long ATTT repeat sequences in intron 1, which may have triggered a rapid gene conversion and/or stabilize the duplicated genes.