The PathHunter ProLabel®/ProLink™ Detection Kit is to be used with PathHunter Cell Lines or cell lines made with ProLabel/ProLink (PL/PK) expression or cloning vectors. The kit is easy-to-use and has been successfully run in both 96- well and 384-well microplate format. The resulting signal is chemiluminescent and is read with any standard plate reader. PathHunter products utilize the Enzyme Fragment Complementation (EFC) technology for studying proteinprotein interactions, protein translocation, receptor trafficking, and receptor internalization, all of which involve the complementation of two β-galactosidase (β-gal) fragments. The larger β-gal fragment is called Enzyme Acceptor (EA) and the smaller fragment is termed Enzyme Donor (ED; also known as ProLink or ProLabel). The two fragments are inactive when apart. However, when they complement, they form a functional enzyme that hydrolyzes the substrate to generate a chemiluminescent signal. The detection reagents contain the EA fragment of β-gal, and therefore must be used in conjunction with cells that express PL or PK in order to obtain a detectable signal.