The mucin genes encode epithelial glycoproteins, some of which are secreted and some membrane bound. Each of the genes contains at least one large domain of tandemly repeated sequence that encodes the peptide sequence rich in serine and/or threonine residues, which carries most of the O-linked glycosylation .

MUC3 gene, demonstrating that it encodes a transmembrane mucin and is subject to alternative splicing to a form lacking 1 EGF-like domain and the transmembrane domain. Structural homology of the human MUC3 sequence with that of rat and mouse Muc3 indicated that it is closely related to the rodent proteins and is likely to be involved in ligand binding and intracellular signaling.