Isolation and characterization of complementary DNAs encoding human pregnancy-specific beta 1-glycoprotein

Area of Science:

• Biochemistry
• Molecular Biology
• Genetics

Background:

• Human placenta contains pregnancy-specific beta 1-glycoprotein (PS beta G), a complex of glycoproteins with varying molecular masses.
• Heterogeneity in PS beta G is further supported by nonglycosylated polypeptides identified through immunoprecipitation.

Purpose of the Study:

• To investigate the structural relationships among different PS beta G protein variants.
• To confirm the identity of proteins encoded by isolated cDNA clones.

Main Methods:

• Isolation and sequencing of two human placental cDNA clones (PSG16 and PSG93) encoding PS beta G.
• In vitro translation and immunoprecipitation using antiserum to placental PS beta G.
• Northern hybridization, primer extension, and S1 nuclease mapping to analyze PS beta G mRNAs.
• Comparison of predicted amino acid sequences with experimentally determined peptide sequences.

Main Results:

• Two cDNA clones, PSG16 and PSG93, were sequenced, showing high identity with a minor difference in the 3'-coding region, potentially leading to PS beta G variants with 417 or 419 amino acid residues.
• The calculated molecular masses of encoded polypeptides (46.9 and 47.2 kDa) align with the major nonglycosylated PS beta G (48 kDa).
• Analysis revealed two PS beta G mRNAs (2200 and 1700 bases) and heterogeneous 5' termini in PS beta G mRNAs.

Conclusions:

• The isolated cDNA clones represent human PS beta G, providing insights into its structural heterogeneity.
• The findings confirm the identity of the encoded proteins and elucidate aspects of PS beta G gene expression in the human placenta.