lacZ(Δα) corresponds to an enzymatically inactive fragment of the β-galactosidase enzyme encoded by Ecol\lacZ, lacking amino acid residues 11-41. If the lacZ(Δα) split enzyme fragment is brought into close association with the complementary lacZ(Δω) split enzyme fragment in vivo, by fusing each split fragment to interacting peptides, a catalytically active enzyme may be reconstituted, allowing detection of the protein-protein interaction (PMID:9237989).