Glucocorticoid receptors of wild-type and variant mouse lymphoma cells

Glucocorticoid receptors of wild-type mouse lymphoma cells and two glucocorticoid resistant variants of nt- and nti phenotypes, respectively, were investigated. Photoaffinity labelling of receptor complexes with a radiolabelled glucocorticoid of high affinity enabled us to analyse crude receptor preparations by SDS gel electrophoresis. Wild-type and nt- receptors yielded radiolabelled polypeptide bands of 98,000 mol. wt while nti receptors had a mol. wt of 42,000. Monoclonal antibodies raised against purified rat liver glucocorticoid receptors reacted with wild-type and nt- receptors but not with nti receptors. Partial proteolysis of wild-type receptors with alpha-chymotrypsin resulted in a fragment of 39,000 mol. wt which contained the steroid binding site but had increased affinity for DNA indistinguishable from nti receptors. Mild proteolysis with trypsin yielded smaller fragments which contained the steroid binding site but did not bind to DNA. A model of the wild-type receptor is discussed.