Primary structure of human carcinoembryonic antigen (CEA) deduced from cDNA sequence.

The cDNAs corresponding to the mRNA encoding a polypeptide which is immunoreactive with the antisera specific to carcinoembryonic antigen (CEA) (1) are cloned. The amino acid sequences deduced from the nucleotide sequences of the cDNAs show that it is synthesized as a precursor with a signal peptide followed by 668 amino acids of the putative mature CEA peptide, whose N-terminal 24 amino acids and amino acids 286 to 295 exactly coincide with those known for N-terminal sequences of CEA (2) and NFA-1 (3), respectively. The first 108 N-terminal residues are followed by three very homologous repetitive domains of 178 residues each and then by 26 mostly hydrophobic residues which probably comprise a membrane anchor. Each repetitive domains contains 4 cysteines at precisely the same positions and as many as 28 possible N-glycosylation sites are found in the CEA peptide region agreeing with high carbohydrate content of purified CEA.