Estrogen Receptor of Cow Uterus 1

Abstract

"8S" estrogen receptor-forming factor [("8S"ER)-FF], a cytoplasmic factor of cow uterus, which binds specifically with native "4S" estrogen receptor (ER) to give "8S" ER under hypotonic (low salt) conditions was dissociated in the presence of 0.4 M NaSCN into two kinds of subunits designated as component A and component B. Characterization of components A and B was performed. The Stokes radius and molecular weight of component A were estimated to be around 37 A and 58,000, respectively. Those of component B were estimated to be around 18.5 A and 13,700, respectively. These components did not bind with estradiol, and underwent molecular assembly depending on the salt concentration of the medium to give complexes, which, in turn, bound with native "4S" ER to give ERs with higher sedimentation coefficients. Component A [designated as "5S" ER-forming factor, ("5S"ER)-FF] bound with native "4S" ER to give "5S" ER, which was stable under hypertonic (0.4 M KCl) conditions. Under hypotonic conditions, component B formed a hexamer [designated as "6S" ER-forming factor ("6S"ER)-FF], which bound with native "4S" ER to give "6S" ER. "4S" ER was dissociated from "6S" ER under hypertonic conditions. ("8S"ER)-FF was shown to be a 1 : 1 complex of component A and the hexamer of component B. These factors [("5S"ER)-FF, ("6S"ER)-FF and ("8S"ER)-FF] which bind specifically with native "4S" ER to give ERs with higher sedimentation coefficients were designated as estrogen receptor-binding factors (ERBFs).