PathHunter® RTK Activity cell lines are engineered to express a fusion of the intracellular catalytic domain from the target RTK and the extracellular ligand binding domain of EGFR. This fusion protein is tagged with ProLink™ (PK). The cells co-express an Enzyme Acceptor (EA) tagged SH2 domain. Ligand induced cross-phosphorylation of the PK-tagged fusion protein leads to SH2-EA recruitment, forcing complementation of the two β-galactosidase enzyme fragments (EA and PK). The resulting functional enzyme hydrolyzes substrate to generate a chemiluminescent signal. These cells have been modified to prevent long term propagation and expansion using a proprietary compound that has no apparent effect on assay performance.