Structure of the pig sterol 14alpha-demethylase (CYP51) gene and its expression in the testis and other tissues

A cDNA coding sterol 14alpha-demethylase (CYP51), which was isolated from a pig liver cDNA, contained a 1,512 bp open reading frame and a 758 bp 3'-untranslated region. The deduced amino acid sequence was 94% identical to those of human and rat CYP51s. The pig CYP51 gene spanned about 21 kb and was divided into 10 exons. The sites of exon-intron junctions were completely identical to those in the human and rat CYP51 genes. Five GC boxes, but not a TATA box, were found in the 5'-flanking region of the gene, and cyclic AMP and sterol responsive elements were also found in this region. The main transcription start site determined with the 5'-RACE method with poly(A)(+) RNA from the liver and testis was located at 143 nucleotides upstream from the initiation codon in both tissues. Northern blot analysis revealed that an approximately 2.4 kb mRNA, which is produced through the use of a polyadenylation signal (AATAAA) located at 740 nucleotides downstream of the stop codon, was expressed in all the tissues examined in pigs: The mRNA levels were much higher in the liver and testis than in the kidney, lung, and epididymis. Furthermore, after the onset of spermatogenesis, a smaller size of mRNA (about 1.8 kb) was found in the testis but not in the epididymis. The 1.8 kb mRNA was produced through the use of an unusual polyadenylation signal (AAGAAA) located at 28 nucleotides downstream of the stop codon.