For several years, my laboratory has been studying the mechanism of action of the glucocorticoid class of steroid hormones. My particular interest centers on the cytotoxic and growth inhibitory effects of these drugs which are exploited in cancer chemotherapy. Our work has focused on the study of the interaction of glucocorticoids with their specific receptors. Recently, we have developed considerable evidence that the ability of the receptor to bind steroid is controlled by a phosphorylation mechanism. This observation has, in turn, led to the concept that subsequent transformation of the steroid-receptor complex to the nuclear-binding state may involve a dephosphorylation reaction. In the work of this proposal we will test two unique models presented to explain the transformation reaction. Our approach will exploit the newly discovered effect of molybdate as a reversible clocker of transformation in order to achieve purification of the untransformed glucocorticoid-receptor complex. We will transfer 32p from ATP to the receptor and then use the partially purified untransformed radiolabeled steroid-receptor complex as a substrate for determining whether or not there is a transforming enzyme that acts as a protein phosphatase. We will determine if transformation also involves the dissociation of a smaller molecular weight component from the receptor complex, and if so, that component will be purified and characterized.