CHARACTERIZATION OF THE GENE ENCODING A FOLATE-BINDING PROTEIN EXPRESSED IN HUMAN PLACENTA - IDENTIFICATION OF PROMOTER ACTIVITY IN A G-RICH SP1 SITE LINKED WITH THE TANDEMLY REPEATED GGAAG MOTIF FOR THE ETS ENCODED GA-BINDING PROTEIN

The gene encoding a folate-binding protein (FBP) expressed in human pl acenta has been cloned by screening a genomic library with the KB cell FBP complementary DNA. This gene, contained in a 10-kilobase EcoRI fr agment of this genomic clone, has 5 exons, 4 introns, the AATAA polyad enylation signal in the 3'-untranslated region, and a 5'-flanking sequ ence which contains the promoter elements, all of which span approxima tely 5 kilobases. Transcription initiation was mapped by RNase protect ion to a site 73 base pairs downstream from a G-rich sequence linked t o a tandemly repeated GGAAG sequence which is a motif that the ets onc ogene encoded GA-binding protein (GABP) transcription factor binds, Ge l shift and supershift mobility assays indicate that the G-rich sequen ce and the ets motif bind specifically to SP1 and GABP, respectively. These cis regulatory elements in tandem drive expression of the chlora mphenicol acetyltransferase reporter gene in transiently transfected m ouse 3T3 cells. The location of these elements upstream of transcripti on initiation in this gene, which lacks an appropriately located TATA box promoter, indicates that this SP1-GA binding region most probably regulates expression of this placental FBP. The gene encoding this pla cental FBP has been assigned the FBP/PL-1 gene because it is a member of a multigene family that includes a gene encoding a FBP expressed in both EE cells and placenta and its unprocessed pseudogene.