Cloning and nucleotide sequence analysis of the dog insulin gene. Coded amino acid sequence of canine preproinsulin predicts an additional C-peptide fragment.

A 4.0-kilobase HindIII/EcoRI-cleaved dog genomic DNA fragment was shown to contain the dog insulin gene by restriction mapping using a human insulin cDNA probe. This fragment was subsequently cloned in a lambda vector, and the nucleotide sequence of the dog insulin gene was determined. As in several other species, the insulin gene of the dog is interrupted by two intervening sequences, one of 151 base pairs located in the 5' untranslated region and the other of 264 base pairs occurring within the codon of the 7th amino acid of the C-peptide. Translation of the nucleotide sequence in one frame revealed the primary structure of canine preproinsulin. An interesting feature of the coded amino acid sequence is that it predicts a C-peptide of 31 amino acids, 8 residues longer than that reported by Peterson et al. (Peterson, J. D., Nehrlich, S., Oyer, P. E., and Steiner, D. F. (1973) J. Biol. Chem. 247, 4866-4871). The additional octapeptide sequence, Glu-Val-Glu-Asp-Leu-Gln-Val-Arg, is located NH2-terminal to the 23-residue C-peptide sequence described in the earlier report. Its coding sequence is interrupted by the second intervening sequence. The arginine at position 8 suggests that a trypsin-like cleavage may separate the NH2-terminal octapeptide from the remainder of the C-peptide during the post-translational processing of dog proinsulin in the pancreas. The revised C-peptide sequence suggests that the proinsulin C-peptide is more highly conserved in length and overall sequence than was previously supposed.