Fig 3.

Interaction of the CitA sensor kinase with the components of the DcuS/DcuR system according to studies using the bacterial two-hybrid system (BACTH). E. coli BTH101 cotransformed with plasmids in pairs encoding T18-DcuS (pMW429), T25-DcuS (pMW426), T18-CitA (pMW1025), and T25-DcuR (pMW427) were grown to an OD₅₇₈ of 0.5 to 0.7 and tested for ß-galactosidase activity. The strain expressing the pair of leucine zipper proteins, T25-Zip (pKT25) plus T18-Zip (pUT18C), was used as a positive control for two cytosolically located interacting proteins. The level of 55 Miller units is the background activity obtained for noninteracting proteins like the T25-Zip and T18-DcuS pair.