DiscoverX develops, commercializes and manufactures reagents and assay kits for the drug discovery market. Their focus is on lucrative protein target classes, such as G-protein-coupled receptors and kinases. The company is built around a proprietary technology called enzyme fragment complementation or EFC which forms the basis of the assays that they design and market. In EFC, two ß-galactosidase fragments are employed which are themselves inactive. One fragment (EA) has an inactivating deletion while the second fragment (ED) has a complementing fragment; in solution where both EA and ED are present, certain pairs of fragments combine spontaneously to form active complexes. Some pairs of fragments interact only weakly and combine to produce enzyme activity only when forced into close proximity by virtue of their attachment to proteins which bind to each other. This property permits evaluation of intracellular protein interactions for use in high throughput screening of drug candidates for their effect on specific cellular pathways. The company offers a wide variety of cell lines that produce such fusion products.