Bacterial One- and Two-Hybrid Assays to Monitor Transmembrane Helix Interactions

In transenvelope multiprotein machines such as bacterial secretion systems, protein-protein interactions not only occur between soluble domains but might also be mediated by helix-helix contacts in the inner membrane. Several assays have been therefore developed to test homotypic and heterotypic interactions between transmembrane α-helices in their native membrane environment. Here, we provide detailed protocols for two genetic assays, TOXCAT and GALLEX, which are based on the reconstitution of dimeric regulators allowing the control of expression of reporter genes.