Structure and gene organization of bovine neuromedin K precursor

cDNA and genomic DNA clones for the precursor of a mammalian neuropeptide tachykinin, neuromedin K, have been isolated and characterized by molecular cloning and sequence analysis. The deduced amino acid sequence indicates that the bovine neuromedin K precursor (preprotachykinin B) consists of 126 amino acid residues including a putative signal peptide. There are two preprotachykinin B mRNAs that differ only at the 5' extremity of the untranslated regions. The major mRNA species is encoded by seven exon sequences, while the minor species includes two extra 5' exon sequences and lacks the 5' terminus of the first exon sequence for the major mRNA species. The above gene organization for the major preprotachykinin B mRNA closely resembles that for the preprotachykinin A mRNA encoding the precursor for substance P and substance K. This structural resemblance strongly suggests that the two preprotachykinin genes have evolved from a common ancestor gene. Furthermore, we have found that the preprotachykinin A and B mRNAs markedly differ in their major expression sites. The results described thus indicate that the diversity of the mammalian tachykinin system has been acquired through various cellular mechanisms including gene duplication and differential expression of duplicated genes.