Fig. 5

MafB and mafI genes code for toxins and cognate immunity proteins, respectively. a The recombinant C-terminal, putatively toxic domains (TD) of MafB2_MGI-2 and MafB_MGI-3 and the immunity proteins MafI2_MGI-2 or MafI_MGI-3 of strain B16B6 were expressed in E. coli strain BL21 (DE3) and survival was determined. Expression of the MafB TD fragments was induced or repressed with arabinose or glucose, respectively, as indicated on top of the figure and expression of the mafI genes was induced with IPTG when the corresponding plasmids were present. After overnight incubation, 20 μl of the bacterial suspensions were spread on half of an LB agar plate containing appropriate antibiotics, and the plates were incubated overnight at 37 °C. b MafI specifically interacts with the C-terminal TD of the cognate MafB. BL21 (DE3) cells co-expressing a Flag-tagged C-terminal MafB TD and a His-tagged MafI were disrupted by sonication, and the lysate was mixed with Ni²⁺ NTA resin. Aliquots of resin-bound and unbound fractions were analyzed by Western blotting with anti-Flag and anti-His monoclonal antibodies