Disorganization and in vitro assembly of the constituents of the cytoplasmic estrogen receptor system of cow uterus.

Analysis of estrogen receptor-binding factors (ERBFs) under isotonic (0.15 M KCl) conditions showed the presence of a factor designated as "7S" estrogen receptor-forming factor [("7S" ER)-FF], which binds with native "4S" estrogen receptor (ER) to form "7S" ER, besides the previously described component B and its hexamer ["6S" ER-forming factor, ("6S" ER)-FF]. Under hypertonic (0.4 M KCl) conditions at lower temperature (4 degrees C), ("7S" ER)-FF and the monomer of component B were present. Under hypertonic conditions at higher temperature (25 degrees C), ERBF existed as component A ["5S" ER-forming factor, ("5S" ER)-FF] and component B. ("7S" ER)-FF was estimated to be a 1 : 2 complex of component A and component B. Under isotonic conditions, approximately 30% of the cytoplasmic ER was "4S" form, and the rest was "6S" and "7S" forms. "5S" ER, "6S" ER, "7S" ER, and "8S" ER were reconstituted from partially purified native "4S" ER and the corresponding ERBFs. "5S" ER was estimated to be a 1 : 1 complex of native "4S" ER and ("5S" ER)-FF. "6S" ER was estimated to be a 1 : 1 complex of native "4S" ER and ("6S" ER)-FF. "7S" ER was estimated to be a 1 : 1 complex of native "4S" ER and ("7S" ER)-FF. "8S" ER was estimated to be a 1 : 1 complex of native "4S" ER and the "8S" ER-forming factor [("8S" ER)-FF] previously described, in which component A is bound to "4S" ER not directly, but via component B. A schematic molecular model of the in vitro dissociation and assembly of the constituents of the cytoplasmic ER system of cow uterus is presented.