Determination of transcription start sites in the human estrogen receptor gene and identification of a novel, tissue-specific, estrogen receptor-mRNA isoform

The human estrogen receptor (ER) gene has previously been shown to be transcribed from two different promoters which are expressed in a cell- and tissue-specific manner. Whereas the transcriptional start sites of the proximal promoter are known, the transcriptional initiation site(s) of the distal promoter has not been identified. In this study, a PCR-based technique was used to isolate the 5' ends of ER cDNAs from different human cell lines and tissues. Using this technique the positions of the transcription initiation sites in the distal promoter were determined. In addition a novel 5' untranslated exon was isolated from human liver. These results demonstrate that the human ER gene contains a third, previously not described promoter which appears to be predominantly expressed in liver.