FIG. 1.

Detection of membrane protein associations with the BACTH system. (a) Proteins of interest X and Y are genetically fused to the two complementary fragments, T25 and T18, from the catalytic domain of B. pertussis AC and coexpressed in E. coli cya cells. (b) Interaction between the two hybrid proteins results in functional complementation between the T25 and T18 fragments, leading to cAMP synthesis. cAMP, upon binding to the catabolite activator protein (a transcriptional regulator) triggers the expression of E. coli catabolic operons, allowing the bacteria to utilize sugars such as lactose and maltose. Efficiencies of complementation can be determined by measuring β-galactosidase activities in the transformed cells.