Watanabe S, Chou J Y
Human Genetics Branch, National Institute of Child Health and Human Development, Bethesda, Maryland 20892.
J Biol Chem. 1988 Feb 5;263(4):2049-54.
Pregnancy-specific beta 1-glycoprotein (PS beta G) isolated from human placenta consists of a set of at least three glycoproteins with apparent molecular masses of 72, 64, and 54 kDa, respectively. This heterogeneity is confirmed by the detection of three nonglycosylated polypeptides of 50, 48, and 36 kDa, which can be immunoprecipitated by antiserum to placental PS beta G obtained by in vitro translation of placental poly(A)+ RNA. To examine the structural relationships between these proteins, two cDNA clones of 1912 base pairs (PSG16) and 2131 base pairs (PSG93) encoding human PS beta Gs were isolated from a human placental lambda gt11 cDNA library. The sequenced portions of these two cDNAs are identical with the exception that clone PSG93 contains an additional 86 base pairs at the end of the common 3'-coding region. This insertion could result in the generation of a PS beta G species of 419 amino acid residues instead of the 417 amino acid residues predicted by the sequence of clone PSG16. The calculated molecular masses of the two polypeptides encoded by PSG16 and PSG93 are 46.9 and 47.2 kDa, close to the size of the major nonglycosylated PS beta G of 48 kDa. The identity of proteins coded for by these cDNA clones was confirmed by comparing the predicted amino acid sequences to sequences determined from endoproteinase Lys-C peptides obtained from human placental PS beta G. Two placental PS beta G mRNAs of 2200 bases (major) and 1700 bases (minor) have been detected by Northern hybridization analysis. Primer extension and S1 nuclease mapping experiments demonstrated that PS beta G mRNAs have heterogeneous 5' termini.
从人胎盘中分离出的妊娠特异性β1-糖蛋白（PSβG）由一组至少三种糖蛋白组成，其表观分子量分别为72、64和54 kDa。通过检测50、48和36 kDa的三种非糖基化多肽证实了这种异质性，这些多肽可被针对通过胎盘多聚腺苷酸加尾RNA体外翻译获得的胎盘PSβG的抗血清免疫沉淀。为了研究这些蛋白质之间的结构关系，从人胎盘λgt11 cDNA文库中分离出两个编码人PSβG的1912个碱基对（PSG16）和2131个碱基对（PSG93）的cDNA克隆。这两个cDNA的测序部分相同，只是克隆PSG93在共同的3'编码区末端含有另外86个碱基对。这种插入可能导致产生一种419个氨基酸残基的PSβG物种，而不是由克隆PSG16的序列预测的417个氨基酸残基。由PSG16和PSG93编码的两种多肽的计算分子量分别为46.9和47.2 kDa，接近主要的48 kDa非糖基化PSβG的大小。通过将预测的氨基酸序列与从人胎盘PSβG获得的内肽酶Lys-C肽确定的序列进行比较，证实了这些cDNA克隆编码的蛋白质的同一性。通过Northern杂交分析检测到两种2200个碱基（主要）和1700个碱基（次要）的胎盘PSβG mRNA。引物延伸和S1核酸酶图谱实验表明，PSβG mRNA具有异质性的5'末端。
