FIG. 1.

Construction of pHSG576 plasmids containing artificial genes for the expression of covalently linked MdtB and/or MdtC transporters. The mdtB or mdtC gene, connected to a downstream linker sequence coding for the horizontal helix of AcrB (29), was made as a SalI-SacI, SacI-HindIII, or HindIII-SphI sequence depending on whether it was intended as the first, second, or third unit, respectively, and was cloned into the MCS site of pHSGS, the first unit together with the upstream mdtA gene. For the final constructs, only pHMA-BBB10 and pHMA-CCC10 are shown here as examples. The artificial genes for covalently linked dimers and trimers are underlined in the names of the plasmids. For other constructs, see Fig. 3A, and for details, see the text.