THE STRUCTURE OF GLUCOCORTICOID RECEPTORS

The glucocorticoid receptor of mouse thymic lymphoma cells was investi gated. The receptor-hormone complex in cytosolic extracts has a Stokes ' radius of 82 angstrom and M(w) approximately 330 kDa. In the presenc e of salt at high concentrations, however, the receptor-complex has a Stokes' radius of 60 angstrom and M(w) approximately 120 kDa. This rec eptor form is able to interact with DNA. Chemical cross-linking was us ed to stabilize the high molecular weight receptor structure against s ubunit dissociation and this was found to prevent receptor activation to DNA binding. The affinity labeled receptor was submitted to progres sive cross-linking and the intermediate cross-linked forms were analyz ed. 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 prot ein hsp90 and an additional protein subunit. The latter was unequivoca lly identified by immunochemical techniques as the 59 kDa protein p59. The 70 kDa heat shock protein was found not to be a bona fide recepto r component but was a contaminant of our immunopurification procedure. Cross-linking studies also showed that the receptor exists in the hig h molecular weight form in intact cells and in the absence of hormone.