FIG 7.

Interaction of the DctB, DctA, and DctS proteins. The arrows between the different proteins are labeled to show whether the interaction experiments using the BACTH, mSPINE, and mHPINE experiments were positive (+) or negative (−). There was a strong interaction between DctB and DctS, and the mSPINE and mHPINE assays showed a strong interaction of DctA with the sensor kinase DctS. No interaction was detected between DctB and DctA, suggesting that the transport of C₄-dicarboxylates by DctA is independent of the presence of the binding protein DctB. In addition to the BACTH assays shown in Fig. 2 and Fig. 3B, the assay was used to analyze the interaction between DctS and DctA, but none of the T18 and T25 fusion pairs showed β-galactosidase activity above background levels (data not shown). In the BACTH assay, sterical hindrances of potential interaction partners can lead to a false-negative result (11), which is a common problem with membrane proteins which can move and rotate only in two dimensions.