CHARACTERIZATION OF AN ESTROGEN-RESPONSIVE ELEMENT IMPLICATED IN REGULATION OF THE RAINBOW-TROUT ESTROGEN-RECEPTOR GENE

We previously reported that the expression of the rainbow trout estrog en receptor (rtER) gene is markedly increased by estradiol (E(2)). In this paper, we have used transient transfection assays with reporter p lasmids expressing chloramphenicol acetyl transferase (CAT), linked to 5' flanking regions of the rtER gene promoter, to identify cis-elemen ts responsible for E(2) inducibility. Deletion analysis localized an e strogen-responsive element (ERE), at position +242, with one mutation on the first base compared with the consensus sequence. This element c onfers estrogen responsiveness to CAT reporter linked to both the herp es simplex virus thymidine kinase promoter and the homologous rtER pro moter. Moreover, using a 0.2 kb fragment of the rtER promoter encompas sing the ERE and the rtER DNA binding domain obtained from a bacterial expression system, DNase I footprinting experiments demonstrated a sp ecific protection covering 20 bp (+240/+260) containing the ERE sequen ce. Based on these studies, we believe that this ERE sequence, identif ied in the rtER gene promoter, may be a major cis-acting element invol ved in the regulation of the gene by estrogen.