As a first step towards understanding the mechanism underlying the differential gene expression of the two variants of the rat proteinase-inhibitor a1-inhibitor 3 (a1-I3) corresponding genomic clones were isolated. The 100% similarity between the sequence of one genomic clone and that of the a1-I3 variant I cDNA strongly suggested that its 5'-sequence represented the upstream region of the corresponding gene. Several putative cis-regulatory elements were identified as well as a polypyrimidine tract located between the transcription start site of the a1-I3 variant I mRNA and the AUG codon. The polypyrimidine tract functions as a positive cis-element in a heterologous promoter. By electrophoretic mobility shift assays (EMSA) we have shown that a GST (glutathione S-transferase) fusion of the rat polypyrimidine tract binding protein (PTB) has a high affinity for the pyrimidine-rich sense strand but not for the complementary sequence of the 5'-untranslated region of the a1-I3 variant I gene.
- α 1 -inhibitor 3
- Acute phase protein
- Polypyrimidine-tract binding protein