The PathHunter® eXpress Nuclear Translocation assay format detects translocation of target NHRs into the nucleus using Enzyme Fragment Complementation. The cells have been engineered to express two complementary fragments of β-galactosidase that are localized to different cellular compartments: the smaller ProLabel® (PL) fragment is fused to the NHR and localized in the cytoplasm; the larger enzyme acceptor (EA) fragment is localized in the nucleus. Activation of the NHR induces receptor translocation to the nucleus, forcing complementation of the PL and EA fragments. Activity of the resulting fully formed β-galactosidase enzyme is detected using a chemiluminescent substrate. These cells have been modified to prevent long term propagation and expansion using a proprietary compound that has no apparent effect on assay performance.