CHARACTERIZATION OF THE RAT GLUTATHIONE-S-TRANSFERASE YC(2) SUBUNIT GENE, GSTA5 - IDENTIFICATION OF A PUTATIVE ANTIOXIDANT-RESPONSIVE ELEMENT IN THE 5'-FLANKING REGION OF RAT GSTA5 THAT MAY MEDIATE CHEMOPROTECTION AGAINST AFLATOXIN B-1

We have isolated and characterized genomic DNA encoding the rat glutat hione S-transferase Yc(2) subunit. This protein is now referred to as rGSTA5 and is noteworthy because of its high activity towards aflatoxi n B-1-8,9-epoxide, its marked inducibility by chemoprotectors, its sex -specific regulation, and its overexpression in hepatoma and preneopla stic nodules. The rGSTA5 gene, which was isolated on two overlapping b acteriophage lambda clones, is approx. 12 kb in length and, unlike oth er class Alpha genes described to date, it comprises six exons. The tr anscription start site has been identified 228 bp upstream from the AT G translational initiation codon, and is situated 51 bp downstream fro m a consensus TATA-box. Deletion analysis, using luciferase reporter c onstructs, has shown that the region between -177 bp and +65 bp from t he transcriptional start site contains a functional promoter. Computer -assisted analysis of the upstream sequence has indicated the presence of an antioxidant-responsive element (ARE), and several elements thou ght to be required for tissue-specific expression of the enzyme. In ad dition, several putative oestrogen-responsive half sites were observed in both upstream and intronic sequences.