Recognition of two forms of the estrogen receptor in the guinea-pig uterus at different stages of development by a monoclonal antibody to the human estrogen receptor. Dynamics of the translocation of these two forms to the nucleus.

Two forms of the estrogen receptor were recognised in the cytosol fraction of fetal uterus of guinea pig by a monoclonal antibody (D547Sp gamma) to the human estrogen receptor. It was observed that 60-65% of the total cytosol estrogen receptor (the alpha form) was bound to the antibody, increasing its sedimentation coefficient in a high ionic strength sucrose gradient (10-30% w/v sucrose, 0.4 M KCl) from 4.5 S to 7.4 S. The remaining fraction (the beta form) has the classical sedimentation coefficient of 4.5 S. Dynamic studies of the translocation in vitro of the cytosol receptor to the nucleus as a function of time have shown that the alpha form decreases sharply while the beta form is slightly affected when the cytosol was incubated with the nuclei. In contrast only one form, which is bound totally to the antibody, was found in the nuclear fraction. In addition, the presence of these two forms of the cytosol estrogen receptor was also demonstrated in newborn and immature animals.