Interaction of calf uterine estrogen receptors with chicken target cell nuclei

The calf uterine estrogen receptor (ER) was used to study the capacity and the characteristics of the acceptor sites in chicken target cell nuclei. The temperature-activated ER is bound at 0 degrees C with a high affinity to all chicken cell nuclei tested (Kd = 0.4-1.0 nM). The nuclear binding displayed tissue specificity: oviduct greater than liver, heart greater than spleen greater than erythrocytes and was salt-dependent. ER binding to liver nuclei measured in 0.15 M KCl varied between 3000 and 6000 acceptor sites per nucleus. Liver nuclei isolated from estrogen-treated cockerels showed a 2-fold lower binding capacity than nuclei from non-treated chickens. When nuclei were incubated with 3H]ER from embryo liver and increasing concentrations of uterine non-radioactive-ER a progressive inhibition of the binding of the liver ER was found. These experiments suggest that liver and uterine ER compete for a common acceptor site. Liver nuclei charged in vitro with calf uterine ER were digested at 0 degree C with DNAase I and micrococcal nuclease. Both enzymes excised the ER in the form of a chromatin-ER complex. A considerable portion was associated with nucleosomal subunits and a minor fraction was associated with a nuclease-sensitive, protein-poor fraction of the chromatin.