Pregnancy-specific beta 1-glycoprotein: cDNA cloning, tissue expression, and species specificity of one member of the PS beta G family.

Pregnancy-specific beta 1-glycoprotein (PS beta G) is a heterogeneous product of the human syncytiotrophoblast, closely related to the CEA-NCA multigene family. In the present study, immunoscreening was carried out with anti-PS beta G antibodies to isolate cDNA sequences from a placental lambda gt11 expression library. One 1847-bp cDNA clone comprising the major portion of the coding sequence of a putative 48-kd peptide was sequenced and characterized. Hybridization of human genomic DNA to the PS beta G sequence revealed a complex pattern of restriction fragments, a finding well in agreement with the assumption that there are several independent PS beta G genes. A variable PstI band was found in human DNA. Transfer blot analysis of human placental RNA identified transcript of 2.2kb and 1.7kb that appear transiently with increasing levels of expression during gestation. No hybridization of PS beta G cDNA to human RNA from liver, kidney, heart, thyroid, and ovary was observed. In analyses of placental RNA from mouse, goat, sheep, and cow, no corresponding transcripts could be detected, and DNA hybridization under low-stringency hybridization conditions resulted in very faint cross-reacting bands, presumably indicating sequences that were scarcely related. However, PS beta G-specific DNA sequencies with similar restriction patterns were found in primates. These results are compatible with the assumption of late evolutionary development of certain PS beta G sequences.