Association of heat shock protein 90 with the 16 kDa steroid binding core fragment of rat glucocorticoid receptors.

We have recently described a 16 kDa steroid binding core (Thr537-Arg673) of the rat glucocorticoid receptor [Simons et al. (1989) J. Biol. Chem. 264, 14493-14497]. Sedimentation analysis and size exclusion and anion exchange chromatography now suggest that other proteins are associated with the 16 kDa receptor, just as has been seen for the intact 98 kDa receptor. The 16 kDa fragment was also immunoprecipitable with anti-heat shock protein 90 (hsp90) antibody. These results argue that hsp90 binds to the 16 kDa core fragment and directly position the site of hsp90 association between Thr537 and Arg673 of the rat glucocorticoid receptor.