In order to assess the potentiality of Vibrio cholerae ToxR protein and of bacteriophage λ repressor as indicators of the dimerization of periplasmic proteins in Escherichia coli, we have constructed a series of plasmids encoding transmembrane fusion proteins. The amino-terminal part, containing the DNA binding domain of either ToxR or λ repressor, is located in the cytoplasm and acts as reporter for dimerization. As models of periplasmic proteins we have used alkaline phosphatase (a dimer) and β- lactamase (a monomer). Both the expression level and the distance between the transmembrane segment and the periplasmic protein substantially affect the activity of the reporter domains.
Jappelli, R., & Brenner, S. (1998). Changes in the periplasmic linker and in the expression level affect the activity of ToxR and λ-ToxR fusion proteins in Escherichia coli. FEBS Letters, 423(3), 371–375. https://doi.org/10.1016/S0014-5793(98)00125-2