Figure 4. SecB/ChAD addiction modules of TAC systems are specific.

(a) Mtb-SecB^TA, VchoA-SecB^TA, Mmet-SecB^TA and Glov-SecB^TA chaperone specificity towards their cognate TA pair. Strain W3110 ΔsecB was co-transformed with plasmid pK6-Mtb-HigBA1, pK6-VchoA-MqsRA, pK6-Mmet-HicAB or pK6-Glov-HigBA and pSE-based plasmids harbouring different SecB-like chaperones as indicated. Double transformants were grown to mid-log phase, serially diluted and spotted on LB–ampicillin–kanamycin agar plates containing arabinose and IPTG inducers as indicated. Plates were incubated at 37 °C overnight. (b) Functional inter-species transfer of SecB/ChAD-specific pairs within TAC systems using antitoxin chimeras. Strain W3110 ΔsecB was co-transformed with pK6-based plasmids containing chimeric TA systems in which the putative ChAD regions have been swapped, and pSE derivatives harbouring different SecB-like chaperones as indicated, and analysed by spot tests as in a.