Salt extractability of nuclear receptor-estrogen complex from the rat uterus

Estrogen receptors in the nuclei of rat uterus were determined 1 or 6 h after the injection of [3H]estradiol. Ratio of 0.4 M KCl-extractable to -resistant receptor-estradiol complex was constant during this time interval. Three consecutive extractions took out about 95% of receptor-estradiol complex either 1 or 6 h after injection. Extraction with KCl before the exchange assay reduced the amount of salt-resistant nuclear receptor-estradiol complex. However, when exchange incubation with [3H] estradiol was done before KCl extraction, salt-resistant receptor-estradiol complex was significantly increased, even after three consecutive extractions.