Our goal is to define the interactions between purified estrogen receptors and their nuclear acceptor sites. Our work will entail purification of the calf uterine estrogen receptor with retention of its DNA binding domain. We have recently modified an estradiol ligand affinity chromatography procedure for a single step apparent purification of 200-400 fold. This receptor preparation will be used for further purification and characterization. The latter includes molecular weight, substructure composition and isoelectric point determinations, oligodeoxynucleotide binding affinities and sensitivity to inhibitors of DNA bindings. The receptor will be used as a reagent to detect high affinity binding sites in DNA alone or in cooperation with chromosomal proteins from target tissues.