CHARACTERIZATION OF THE TRANSCRIPTION START POINT OF THE TROUT ESTROGEN RECEPTOR-ENCODING GENE - EVIDENCE FOR ALTERNATIVE SPLICING IN THE 5'-UNTRANSLATED REGION

The estrogen receptor (ER)-encoding gene (ER) regulates many genes imp licated in the reproductive functions. Moreover, rainbow trout ER (rtE R) is itself up-regulated by its own product. We have used Northern bl ot, RNase protection, primer extension and reverse transcription-polym erase chain reaction (RT-PCR) to study the position of the rtER mRNA t ranscription start point (tsp) in liver. This analysis has revealed th e presence of a tsp positioned at the beginning of the cloned rtER cDN A. Functionality of this tsp was tested in transient transfections in CHO-KI cells. The characterization of the rtER 5' untranslated region (UTR) showed that two transcripts exist in liver which differ in their 5'-UTR. The first one is 100% homologous to the cloned rtER cDNA sequ ence. The other one contains a 41-bp insertion. The isolation and sequ encing of the first intron showed that this insertion arises from alte rnative splicing, due to the use of a splicing site internal to the fi rst intron.