lacZ(Δω) corresponds to an enzymatically inactive fragment of the β-galactosidase enzyme encoded by Ecol\lacZ, consisting of the first 788 amino acid residues. If the lacZ(Δω) split enzyme fragment is brought into close association with the complementary lacZ(Δα) 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).