Novel aromatase transcripts from bovine placenta contain repeated sequence motifs.

Aromatase cytochrome P-450 (Aro) is the major enzyme of estrogen biosynthesis. The aim of the present investigation was the isolation and comparative sequence analysis of the bovine aromatase cytochrome P-450 transcript (bCyp19) from a placental lambda gt10 cDNA library. From three overlapping clones, a total sequence of 5180 bp could be derived, including two polyadenylation sites and signals located next to each other. As found in other species, the open reading frame (ORF) comprises 1509 bp and shows 87, 78 and 78% sequence homology to the coding areas of the human, rat and mouse genes, respectively. The 3'-untranslated region (UTR) of the bovine transcript is about 2-kb longer than that of the human gene (hCYP19). It contains homologous retroposon elements of the bovidae dimer family (BDF) at two different positions, and ends with a sequence motif which also occurs repeatedly within the bovine genome. The 5'-UTR isolated from placenta includes a new sequence upstream from exon II that was not found in cattle or other species so far. We conclude from our data that (i) as found in other species, bCyp19 is likely to be transcribed into different mRNA species, (ii) the bovine 3'-UTR was the target for multiple insertions of repeated sequence motifs, (iii) the unusual length of the bCyp19 transcript is mainly due to the long 3'-UTR, (iv) it includes sequences which are found in humans only on the genomic level, conceivably due to mutational inactivation of a primordial polyadenylation signal (PAS) and (v) the recently used, functional PAS is contributed by a downstream bovine repeat element.