Primary structure of human pepsinogen gene

A recombinant clone, which covers the pepsinogen gene in a single insert, has been isolated by screening a library of human genomic DNA, using a swine pepsinogen cDNA as a probe. Sequence analysis of coding DNA segments of the clone revealed that the pepsinogen gene occupies approximately 9.4-kilobase pairs of the genomic DNA and is separated into nine exons by eight introns of various lengths. The predicted amino acid sequence of human pepsinogen consists of 373 residues and is 82% homologous with that of swine pepsinogen. In addition, the predicted sequence contained a single sequence of 15 amino acid residues at the NH₂ terminus, showing that the protein is synthesized as prepepsinogen. The structure of the gene, in which two homologous sequences including the two active site aspartyl residues of pepsin are present in different coding segments, is in support of the view that the pepsinogen gene evolved by duplication of a shorter ancestral gene.