Structure of the angiotensin I-converting enzyme gene. Two alternate promoters correspond to evolutionary steps of a duplicated gene.

Overlapping genomic clones containing the entire sequence of the human angiotensin I-converting enzyme (ACE) gene were isolated from a lamda phage human DNA library. This gene spans 21 kilobases (kb) and comprises 26 exons, ranging in size from 88 to 481 base pairs. Intron-exon boundaries were sequenced and the relative positions of the exons were mapped. The two different mRNAs transcribed from the ACE gene were assigned to their respective exons. The large endothelial type ACE mRNA (4.3 kb long) is transcribed from exon 1 to exon 26, excluding exon 13. The 3-kb long testicular ACE mRNA is transcribed from exon 13 to exon 26. Exon 13 encodes for the 67 amino acids of the NH2-terminal region of the testicular ACE, whereas downstream exons encode a sequence common to both isozymes. The gene duplication suggested by the internal homology of the endothelial ACE mRNA is now confirmed by the presence of two homologous clusters of eight exons (exons 4-11 and exons 17-24) having similar sizes and codon phases at exon-intron boundaries. The presence of two alternate promoters was investigated by ribonuclease protection assays. The different 5' ends of the two ACE transcripts revealed a promoter for the endothelial ACE mRNA in the 5'-flanking region of the first exon and a promoter for the testicular ACE mRNA situated in intron 12.