The structure of glucocorticoid receptors

The glucocorticoid receptor of mouse thymic lymphoma cells was investigated. The receptor-hormone complex in cytosolic extracts has a Stokes' radius of 82 A and Mw approximately 330 kDa. In the presence of salt at high concentrations, however, the receptor-complex has a Stokes' radius of 60 A and Mw approximately 120 kDa. This receptor form is able to interact with DNA. Chemical cross-linking was used to stabilize the high molecular weight receptor structure against subunit dissociation and this was found to prevent receptor activation to DNA binding. The affinity labeled receptor was submitted to progressive cross-linking and the intermediate cross-linked forms were analyzed. This led to the conclusion that the high molecular weight receptor structure is a hetero-tetramer consisting of one receptor polypeptide of approximately 100 kDa, two molecules of the 90 kDa heat shock protein hsp90 and an additional protein subunit. The latter was unequivocally identified by immunochemical techniques as the 59 kDa protein p59. The 70 kDa heat shock protein was found not to be a bona fide receptor component but was a contaminant of our immunopurification procedure. Cross-linking studies also showed that the receptor exists in the high molecular weight form in intact cells and in the absence of hormone.