Transformation of mammary cytoplasmic glucocorticoid receptor under cell-free conditions

The transformation of glucocorticoid--receptor complex in the cytosol from lactating mouse mammary tissue was studied by using elevated temperature and KCl as promoters of the transformation reaction. The transformed receptor was identified from the nontransformed receptor by the following criteria: (a) increased binding to DNA--cellulose, (b) increased binding to ATP--Sepharose, (c) higher affinity for the steroid as determined by steroid dissociation kinetics, and (d) different sedimentation profiles on sucrose gradients containing KCl and sodium molybdate. A greater percentage of the nontransformed receptor was converted to the transformed state by an increased KCl concentration as opposed to increased temperature. Pretreatment of cytosol with 10 mM sodium molybdate prevented both the temperature- and salt-mediated transformation of the receptor.