The study reports the full sequence of the human tumor-associated polymorphic epithelial mucin (PEM), a large glycoprotein with a high proportion of serine and threonine residues, which are likely to be heavily glycosylated. PEM is expressed on the cell surface of human mammary cells and is aberrantly expressed in tumors. It contains a large domain of variable numbers of 20-amino acid repeat units, making it a variable number tandem repeat (VNTR) locus. The PEM core protein consists of three regions: an amino-terminal region with a signal peptide and degenerate repeats, a major tandem repeat region, and a carboxyl-terminal region with degenerate repeats and a transmembrane domain. The protein is membrane-anchored, as shown by its expression in COS cells. The sequence reveals that PEM is a mucin with a high proportion of serine and threonine residues, which are potential O-glycosylation sites. The presence of a transmembrane domain and a cytoplasmic tail suggests a role in signal transduction or cellular organization. The study also shows that PEM is expressed in the serum of cancer patients and is used in diagnostic and therapeutic applications. The full-length cDNA sequence of PEM was cloned and expressed in mammalian cells, confirming its membrane-anchored nature. The study highlights the importance of PEM as a tumor-associated antigen and its potential as a target for immunotherapy. The sequence analysis also reveals that PEM is a VNTR locus, with significant genetic variation among individuals, making it a valuable marker for genetic studies and cancer research. The study provides insights into the structure and function of mucins, emphasizing the role of glycosylation in their biological activity.The study reports the full sequence of the human tumor-associated polymorphic epithelial mucin (PEM), a large glycoprotein with a high proportion of serine and threonine residues, which are likely to be heavily glycosylated. PEM is expressed on the cell surface of human mammary cells and is aberrantly expressed in tumors. It contains a large domain of variable numbers of 20-amino acid repeat units, making it a variable number tandem repeat (VNTR) locus. The PEM core protein consists of three regions: an amino-terminal region with a signal peptide and degenerate repeats, a major tandem repeat region, and a carboxyl-terminal region with degenerate repeats and a transmembrane domain. The protein is membrane-anchored, as shown by its expression in COS cells. The sequence reveals that PEM is a mucin with a high proportion of serine and threonine residues, which are potential O-glycosylation sites. The presence of a transmembrane domain and a cytoplasmic tail suggests a role in signal transduction or cellular organization. The study also shows that PEM is expressed in the serum of cancer patients and is used in diagnostic and therapeutic applications. The full-length cDNA sequence of PEM was cloned and expressed in mammalian cells, confirming its membrane-anchored nature. The study highlights the importance of PEM as a tumor-associated antigen and its potential as a target for immunotherapy. The sequence analysis also reveals that PEM is a VNTR locus, with significant genetic variation among individuals, making it a valuable marker for genetic studies and cancer research. The study provides insights into the structure and function of mucins, emphasizing the role of glycosylation in their biological activity.