THE 5'-FLANK OF THE RAT ESTROGEN-RECEPTOR GENE - STRUCTURAL CHARACTERIZATION AND EVIDENCE FOR TISSUE-SPECIFIC AND SPECIES-SPECIFIC PROMOTERUTILIZATION

Published data on the rat estrogen receptor (rER) gene have so far pro vided evidence for only one promoter. In contrast, the human ER (hER) gene has been reported to be transcribed from three different promoter s A, B and C. In order to facilitate a more in-depth analysis of the p romoter organization in the rER gene 4.5 kb of its 5' flanking region were isolated. Sequence analysis suggests that the rER gene is transcr ibed from a promoter homologous to promoter B in the hER gene. However , the region corresponding to the human promoter A is much more diverg ent between the species and rapid amplification of cDNA ends (RACE)-PC R as well as RT-PCR experiments support the notion that the rER gene d oes not contain a functional A promoter. Interestingly, a novel rER mR NA isoform containing a previously unknown 5' untranslated exon was is olated by RACE-PCR, suggesting the existence of a second, distal promo ter in the rER gene. Our results show that this ER mRNA isoform C is t he only one expressed in rat liver. It thus appears that the rER gene contains two promoters that are utilized in a tissue-specific fashion.