Molecular studies of human Schwangerschaftsprotein 1 (SP₁)
Schwangerschaftsprotein 1 (SP1) is a carbohydrate rich serum pregnancy protein of apparent molecular weight 80000 - 90000 Da. SP1 can be detected in the serum of pregnant females as early as 7 days after conception and its concentration increases in an almost linear fashion until the 36th week of pregnancy when the level tends to plateau. At term the maternal blood serum level ranges from 95 - 315 mg/l and, based on its disappearance following delivery, its half life is approx. 40hr. The function of Sp1 is unknown but possible roles in carbohydrate metabolism and immunosuppression have been suggested. SP1 has been useful as an early pregnancy test, in monitoring foetal wellbeing and as a marker in the detection of trophoblastic tumours. SP1 is also produced by non-trophoblastic tumours but its clinical use in monitoring these tumours is uncertain. The main aim of this project was to isolate a cDNA copy of the mRNA for Sp1 with a view to analysing the structure and function of this placental glycoprotein. At the outset of this project no amino acid or DNA sequence data was available for Sp1 so attempts were made to construct expression libraries in gtll with a view to isolating an SP1 using polyclonal antibodies. As this proved unsuccessful efforts were concentrated on obtaining amino acid sequence for the protein. Using a limited amount of sequence data oligonucleotides were constructed and used successfully to screen cDNA libraries. An isolated cDNA clone was examined in detail, its nucleotide sequence derived and the protein sequence deduced.