Molecular cloning of human MUC3 cDNA reveals a novel 59 amino acid tandem repeat region.

The human MUC3 gene is highly expressed in small intestine and gallbladder. Thus far only 646 basepairs of its cDNA encoding 17 amino acid repeats have been cloned. In order to further clone the human MUC3 cDNA, a human small intestinal cDNA library was constructed and screened with a cDNA probe encompassing the 17 amino acid tandem repeat region of human MUC3. In two subsequent screenings of the library resulting positive clones were used as probes. In total, 27 partial MUC3 cDNA clones were isolated and sequenced that define a semi-unique region and a novel 177 nucleotide tandem repeat region, located upstream of the region encoding the 17 amino acid tandem repeats. The 177 nucleotide repeat region is at least 5 kb in length and encodes 59 amino acid repetitive peptides with a consensus sequence of VSTTPVASSEASTLSTTPVDTSTPVTTSTQASSSPTTAEGTSMPTSTPSEGSTPLTSMP, that is notably different from the 17 amino acid repeat of MUC3 or any other known mucin repeat.