Demonstration that the 90-kilodalton heat shock protein is bound to the glucocorticoid receptor in its 9S nondeoxynucleic acid binding form.

The 9S molybdate-stabilized form of the glucocorticoid receptor of mouse L cell lysates was immunoadsorbed to protein-A-Sepharose with antiserum directed against the 89-kilodalton chicken heat shock protein (anti-hsp89). In order to achieve this, "free" (nonreceptor associated) hsp90 was first separated from the molybdate-stabilized 9S receptor by sucrose gradient sedimentation. Incubation of the 9S [3H]triamcinolone acetonide-labeled receptor peak with anti-hsp89 results in the immune-specific adsorption of 20% of the specifically bound radioactivity and adsorption of the 100-kilodalton receptor protein, as detected by Western-blotting, using the GR49 antireceptor monoclonal antibody as probe. These observations provide the only direct proof that hsp90 is a component of the 9S form of a steroid receptor.