EVOLUTIONARY ANALYSIS OF THE MULTIGENE PREGNANCY-SPECIFIC BETA(1)-GLYCOPROTEIN FAMILY - SEPARATION OF HISTORICAL AND NONHISTORICAL SIGNALS

The pregnancy-specific beta(1)-glycoproteins (PSG) form a large family of closely related proteins. Using newly developed methods of sequenc e analysis, in combination with protein modeling, we provide a framewo rk for investigating the evolution and biological function of genes li ke the PSG. Evolutionary trees, based on C-terminal sequence, group PS G genes in a manner consistent with their genomic organization. Trees constructed using the N-terminal domain sequences are unreliable as an indicator of phylogeny because of nonneutral processes of sequence ch ange. During duplication of the PSG genes, evolutionary pressures have resulted in a gradient of constrained change across each gene. The N- terminal domains show a nonrandom pattern of amino acid substitutions clustered in the immunoglobulin complementarity-determining region (CD R)-like regions.