Gene structures of pepsinogens A and C.

Pepsinogen is an inactive precursor of pepsin, a typical aspartic proteinases, synthesized in the chief cells of gastric glands. There are two major groups of pepsinogen, namely pepsinogen A (PGA) and pepsinogen C (PGC) (or progastricsin), and each frequently has isozymogens. The relative extents of expression of the two pepsinogens vary among animal species and, moreover, their biosynthesis is known to be affected by such bioactive peptides as gastrin and secretin; however, the regulation mechanism of pepsinogen biosynthesis, hence pepsinogen gene expression is not yet clear. Therefore, it is thought to be of fundamental importance to elucidate the primary structures of the pepsinogen gene for such studies. This report describes the primary structures of human PGA and PGC genes and rat PGC gene. The organization of the genes is essentially the same; each gene was found to be separated into nine exons by eight introns of various lengths, encoding the amino acid sequence of the corresponding prepepsinogen. These results show that these genes are all derived from a common ancestral gene. The 5'-flanking region of human PGA gene, however, was different from those of human and rat PGC genes, whereas those of human and rat PGC genes were similar to each other. Thus, it is suggested that the expression of the PGA and PGC genes are somewhat differently regulated.