cDNA sequence and genomic organization of mouse secretin

A murine insulinoma library was constructed by subtracting glucagonoma cDNAs from insulinoma cDNAs. Comparison of the nucleotide sequence of one of the clones with sequences from the GenBank database showed that it was a member of the secretin family. The clone, 490 bp long, encodes a protein of 133 amino acids consisting of a signal peptide, a N-terminal peptide, secretin, and a C-terminal peptide, which showed 88% and 80% homology with rat and porcine secretin precursor proteins, respectively. The translated secretin peptide showed a unique Met to Thr substitution at position 5 as compared to the secretins from other species. That the Met to Thr substitution was not tumor-related was demonstrated by the fact that an identical sequence was found in cDNA from normal mouse intestine. Studies on the mouse secretin gene revealed that it contains four exons separated by 81 bp, 110 bp, and 96 bp introns.