A 55-kDa Protein (p55) of the Goat Uterus Mediates Nuclear Transport of the Estrogen Receptor: II. Details of the Transport Mechanism

A 55-kDa protein (p55) that mediates the transport of the estrogen receptor (ER) from the cytoplasm to the nucleus has been purified to homogeneity from goat uterine cytosol. Using this pure protein, some of the aspects of the mechanisms associated with the transport of the ER to the nucleus have been elucidated. The mechanism of ER transport into the nucleus can be separated into two steps: the p55-mediated transport and binding of ER to the nuclear membrane, followed by an ATP-dependent, 14-kDa protein(s)-mediated translocation of ER into the nucleus. The p55 has inherent ATPase activity and it is proposed that the energy released during this ATP hydrolysis is utilized in the nuclear transport of the ER.