SUBTLE DIFFERENCES IN HUMAN PREGNANCY-SPECIFIC GLYCOPROTEIN GENE PROMOTERS ALLOW FOR DIFFERENTIAL EXPRESSION

Eleven pregnancy-specific glycoprotein (PSG) genes reside on human chr omosome 19. The sequence of these genes is extremely similar and that similarity extends to their putative control regions. However, the exp ression pattern of each PSG gene differs in the placenta, the primary site of PSG synthesis. To understand the molecular mechanisms underlyi ng differential PSG expression, we characterized promoter elements of six PSG genes. We have shown previously that nucleotides -172 to -34 w ith respect to the translation start site constitute a minimal promote r in the PSG12 gene (class 1). We now show that PSG1-I and PSG3 are al so members of class 1 genes. In contrast, only nucleotides -172 to -80 are necessary for promoter activity in PSG5, PSG6, and PSG11 genes (c lass 2). Class 2 genes contain a perfect Sp1 recognition sequence (CCC CGCCC) at nucleotides -148 to -141 which is necessary for promoter act ivity. Placental cell extracts formed three protein-DNA complexes with nucleotides -172 to -80 of all six PSG genes. One of the components o f these complexes is an Sp1-like molecule. We have previously reported activator sequences within nucleotides -83 to -34 in PSG12. We now sh ow that a 50-kDa protein binds to this region of PSG11, and the result ant complex can be supershifted by a monoclonal antibody to PEA3.