Structure of a bovine gene for P-450c21 (steroid 21-hydroxylase) defines a novel cytochrome P-450 gene family

P-450c21, a cytochrome P-450 enzyme [steroid 21-monooxygenase (steroid 21-hydroxylase), EC 1.14.99.10], mediates the 21-hydroxylation of glucocorticoid and mineralocorticoid hormones in the adrenal gland. The complete sequence of a bovine P-450c21 gene shows it is 3447 base pairs long and contains 10 exons. The intron/exon organization and encoded amino acid sequence indicate that P-450c21 represents a unique family of genes in the P-450 gene superfamily. Primer extension and S1 nuclease protection experiments identified several cap sites for initiation of transcription; the principal cap site produces mRNA with a 5' untranslated region only 11 bases long. S1 nuclease protection experiments confirm that P-450c21 is actively expressed in the adrenal and the testis, an organ not known to secrete 21-hydroxylated steroids.