The hormone binding domain of the mineralocorticoid receptor can regulate heterologous activities in cis.

Steroid receptors are maintained inactive in the absence of cognate ligand partly because of repression by their hormone binding domain (HBD). Proteins complexed with the unliganded HBD of vertebrate steroid receptors, including the heat-shock protein 90, have been implicated as components of a molecular switch. As such, the HBDs of both the glucocorticoid and estrogen receptors have been shown to be autonomous regulatory cassettes which can subject heterologous activities resident on the same polypeptide to hormonal control. We show that the HBD of the mineralocorticoid receptor (MR) carries a similar "protein inactivation" function. Thus, the MR HBD can be used as a movable regulatory domain, a powerful tool for aldosterone regulation of chimeric proteins.