Selective Binding of the Estradiol Receptor to a Region at Least One Kilobase Upstream from the Rat Prolactin Gene

The interaction of the estradiol receptor with cloned DNA fragments from the prolactin gene was investigated using a competitive binding assay. A DNA fragment from the 5′-flanking region of the rat prolactin gene was able to bind the estradiol receptor selectively. DNA fragments representing most of the remaining 10 kb of the prolactin gene showed little or no selective binding to the estradiol receptor. The fragment from the 5′-flanking region which selectively binds the receptor is located between 1.2 and 2.0 kb upstream from the transcription initiation site rather than in a more proximal position as has been observed for the interaction of several other steroid hormone receptors with specific genes. Nucleotide sequence analysis demonstrated that this region of DNA contains two large segments of alternating purine-pyrimidine sequence. One of the alternating purine-pyrimidine regions is very large, containing more than 160 nucleotides of almost perfect poly(dG-dT). Further studies will be required to determine if the receptor interacts specifically with these interesting sequences. However, the ability of the estradiol receptor to bind to an upstream 5′-flanking region of the prolactin gene may be part of the mechanism which allows the receptor to stimulate the transcription of this gene selectively.