Animal and plant cell lysates share a conserved chaperone system that assembles the glucocorticoid receptor into a functional heterocomplex with hsp90.

The hormone-binding domain of the glucocorticoid receptor must be bound to heat shock protein (hsp) 90 for it to have a high-affinity steroid-binding conformation. Cell-free assembly of a glucocorticoid receptor−hsp90 heterocomplex is brought about in reticulocyte lysate by a preformed protein-folding complex containing hsp90, hsp70, and other proteins [Hutchison, K. A., Dittmar, K. D., & Pratt, W. B. (1994) J. Biol. Chem. 269, 27894−27899]. In this “foldosome” system, hsp70 is required for assembly of the receptor−hsp90 complex and concomitant activation of steroid-binding activity [Hutchison, K. A., Dittmar, K. D., Czar, M. J., & Pratt, W. B. (1994) J. Biol. Chem. 269, 22157−22161]. All previous experiments involving cell-free assembly of both receptor−hsp90 and protein kinase−hsp90 heterocomplexes have been carried out with the protein-folding system in rabbit reticulocyte lysate. In this work, we show that concentrated lysates of receptor-free mouse (L cells) and insect (Sf9) cells and also a plant (w...