A NOVEL GLYCOPROTEIN OF THE ASPARTIC PROTEINASE GENE FAMILY EXPRESSEDIN BOVINE PLACENTAL TROPHECTODERM

The pregnancy-associated glycoproteins (PAG 1) that appear in the mate rnal serum of cattle and sheep soon after implantation are apparently inactive members of the aspartic proteinase family. Here we describe t he isolation of a highly abundant cDNA (PAG 2 cDNA) that represents a second member of this gene family which is structurally related to bov ine FAG 1, ovine FAG 1, and pepsin (58%, 58%, and 51% amino acid seque nce identity, respectively). The bovine FAG 2 cDNA was identified in t wo ways. First, the bovine placental library was screened under relati vely nonstringent conditions with an ovine FAG 1 cDNA. The second fort uitous approach employed immunoscreening with an antiserum raised agai nst a partially purified factor that competed with bovine LII for bind ing to the LH receptor on the CL of the ovary. The full-length cDNA (1 258 bp) codes for a polypeptide of 376 amino acids. Bovine FAG 2, unli ke bovine FAG 1, has a catalytic center with a consensus sequence of a mino acids. Its mRNA is expressed in fetal placenta but not in other f etal organs, and is localized to both the mononucleate and binucleate cells of the trophectoderm, whereas FAG 1 is expressed only in binucle ate cells. FAG 2 is synthesized by placental explants as a 70-kDa glyc oprotein that is processed to several smaller molecules. Western blot analysis of culture media developed with epitope selected antibodies t o FAG 2 reveals several bands ranging in apparent M(r) from 31 000-70 000, which correspond in size to the polypeptides present in the prepa ration used for immunization. The function of FAG 2 remains unclear, b ut it could represent one of the poorly characterized gonadotropin-lik e factors described in placental extracts of cattle and sheep.