Plasmids isolated from a mixture of JA300A/pMW119 and JA300A/pAcrB that have been subjected to selection conditions. AcrB was expressed at basal level in lanes 1 and 2 while IPTG was used to induce protein expression in lanes 3 and 4. Lane 2 was subjected to growth selection with n- octane and lane 4 with 1-octanol. M denotes marker. The isolated plasmids were linearized with BamHI and the sizes correspond to those of pAcrB (7.4 kb) and pMW119 (4.2 kb).