ESTROGEN RECEPTORS . AN EVALUATION OF CYTOPLASMIC-NUCLEAR INTERACTIONS IN A CELL-FREE SYSTEM AND A METHOD FOR ASSAY

The estrogen binding protein of the uterine cytoplasmic fraction will cause the specific binding [3H]estradiol to either nuclear or glass pellets when incubated at 25° for 30 min. This interaction between the cytoplasmic fraction and nuclear or glass pellets provides a rapid method for the analysis of the kinetics and the number of cytoplasmic estrogen receptors in a tissue. The ability of uterine cytoplasmic fraction to label any biological nuclear pellet, as well as glass pellets, indicates that this binding capacity of the cytoplasmic fraction is independent of the type of nuclear pellet. Therefore it is unlikely that any specific uterine nuclear factor is required for the nuclear binding observed in this cell-free system. Furthermore the binding observed in this system does not appear to be comparable to that which occurs in intact cells since no 4-5-S nuclear binder could be extracted from the nuclear pellets. © 1969.