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A partial cDNA (pAM1) encoding a major airway mucin glycoprotein with novel tandem repetitive sequence has recently been cloned (Shankar, V., M. S. Gilmore, R. C. Elkins, and G. P. Sachdev. 1994. Biochem. J. 300:295-298). In this article, we report additional new sequence derived by 3'-rapid amplification of cDNA ends technique. The sequence corresponds to a stop codon, 3'-untranslated region of 458 bp, a polyadenylation signal, and poly A+ tail, and represents the extreme carboxy terminus of MUC8. A plasmid construct (pAM3) in pBluescript was generated by in-frame ligation of pAM1 to the 479-bp 3'UTR of MUC8. A 5'-end 325-bp fragment of this cDNA subcloned into the protein fusion and expression vector pET28b(+) was used to generate fusion protein under the control of T7 promoter. The purified fusion protein as well as synthetic peptide corresponding to the MUC8 repeat sequence (TSCPRPLQEGTPGS) were used to raise polyclonal antibodies in rabbits. The antiserum to the fusion protein and to the synthetic peptide reacted with the deglycosylated major tracheobronchial mucin. Immunohistochemical studies using the above antibodies localized the MUC8 protein product to submucosal glands in human tracheal epithelium. Furthermore, the gene from which this cDNA is derived, was mapped to chromosome 12 using DNA from a panel of human-mouse somatic cell hybrids. Fluorescence in situ hybridization was used to assign the regional localization to 12q24.3. Since the eight known human mucin genes map to other chromosomes, we have named this gene MUC8, in accordance with mucin gene nomenclature.