ISOLATION OF 2 COMPLEMENTARY DEOXYRIBONUCLEIC-ACID CLONES FROM A RAT INSULINOMA CELL-LINE BASED ON SIMILARITIES TO KEX2 AND FURIN SEQUENCES AND THE SPECIFIC LOCALIZATION OF EACH TRANSCRIPT TO ENDOCRINE AND NEUROENDOCRINE TISSUES IN RATS

We have identified two rat insulinoma cDNAs that code for proteins homologous to the Kex2 dibasic protease of yeast and the mammalian furin gene product. A 5.0-kilobase (kb) cDNA, termed BDP, coding for a 752-amino acid protein and a 2.5-kb cDNA coding for a 636-amino acid protein, which was found to be the rat equivalent of the human insulinoma PC2 protein, were isolated. The proteins encoded by these clones contain a specific N-terminal signal sequence, indicating that both enter the secretory pathway. Neither protein contains a C-terminal transmembrane domain as is found in kex2 and furin, suggesting that the proteins may be soluble. Both proteins contain regions surrounding the active site residues which show amino acid identities to both kex2 (43% for BDP and 41% for RPC2) and furin (57% for BDP and 53% for RPC2). Probes specific for the mRNAs of each protein were used to localize the expression of each protein in endocrine and neuroendocrine tissues.