Robertson M C, Schroedter I C, Friesen H G
Department of Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada.
Endocrinology. 1991 Nov;129(5):2746-56. doi: 10.1210/endo-129-5-2746.
Late pregnant rat placenta was found to contain a messenger RNA (mRNA) that encodes an additional member of the prolactin-growth hormone family. This polypeptide was detected by hybridization of complementary DNA (cDNA) for rPL-I to a 1 kilobase mRNA transcript in late pregnant rat placenta. A cDNA clone for the new polypeptide was isolated from a phage lambda-gt10 library containing cDNA synthesized from day 18 rat placental mRNA. Sequencing of the day 18 cDNA clone revealed that it was most closely related structurally to rPL-I and at the amino acid terminal was identical to the rPL-I variant (rPL-Iv). The sequence of rPL-Iv (223 amino acids) is 85% homologous to rPL-I (230 amino acid). There are 71 base pair changes (85% nucleotide homology) between rPL-Iv and rPL-I which are not confined to any specific region of the molecule and which result in 36 amino acid changes. In vitro translation of rPL-Iv mRNA produced by transcription of the cDNA template yielded a 26 kilodalton polypeptide, the size of the expected precursor protein. In situ hybridization studies indicated that mRNA for rPL-Iv was present primarily in cytotrophoblasts of the basal zone as early as day 15 of gestation with some hybridization in a few giant cells as well.
研究发现，妊娠晚期大鼠胎盘含有一种信使核糖核酸（mRNA），它编码催乳素-生长激素家族的另一个成员。通过将催乳素相关蛋白I（rPL-I）的互补脱氧核糖核酸（cDNA）与妊娠晚期大鼠胎盘的1千碱基mRNA转录本杂交，检测到了这种多肽。从一个λ噬菌体gt10文库中分离出了这种新多肽的cDNA克隆，该文库包含从第18天大鼠胎盘mRNA合成的cDNA。对第18天cDNA克隆的测序表明，它在结构上与rPL-I最为密切相关，并且在氨基酸末端与rPL-I变体（rPL-Iv）相同。rPL-Iv（223个氨基酸）的序列与rPL-I（230个氨基酸）有85%的同源性。rPL-Iv和rPL-I之间有71个碱基对的变化（85%的核苷酸同源性），这些变化并不局限于分子的任何特定区域，并且导致了36个氨基酸的变化。通过对cDNA模板进行转录产生的rPL-Iv mRNA的体外翻译产生了一种26千道尔顿的多肽，即预期前体蛋白的大小。原位杂交研究表明，早在妊娠第15天，rPL-Iv的mRNA主要存在于基底部的细胞滋养层中，在一些巨细胞中也有一些杂交信号。
