Human pregnancy-specific beta 1-glycoprotein: a new member of the carcinoembryonic antigen gene family.

The amino acid sequence of human pregnancy-specific beta 1-glycoprotein (PS beta G) as deduced from the cDNA sequence contains two repeated protein domains (1a and 2a) of 93 amino acids each. PS beta G shows strong homology to human carcinoembryonic antigen (CEA) at both nucleotide and amino acid levels. CEA contains eight domains including a N-terminal domain, three repeated domains (I, II, and III), each containing two subdomains (A and B), and a hydrophobic carboxyl-terminal domain. PS beta G contains a CEA-like N-terminal domain, two repeated domains similar to the A subdomains of CEA which is followed by a domain (1b) similar to the B subdomains of CEA, but lacks a hydrophobic carboxyl-terminal domain. The positions of the cysteine residues in each domain also are conserved, indicating that PS beta G and CEA are two members of the same gene family.