Estrogen receptors in the rat uterus. Studies on the interaction of cytosol and nuclear binding sites.

Studies on the interrelationship of binding sites for estrogens found in cytosol and nuclear fractions of the rat uterus show that 17/3-estradiol is f&t associated with a protein (9 S) present in the cytosol. The estrogen subsequently moves into the nucleus where it is bound to a protein (5 S) which can be extracted from the chromatin. Simultaneously with the movement of the estrogen into the nucleus, the binding protein of the cytosol disappears or loses its ability to bind estrogen. These and other experiments are discussed in terms of a hypothetical model in which estrogen binds to a cytosol receptor protein, bringing about a change in its conformation and its subsequent movement into the nucleus.