FIG. 1.

Physical maps and construction of plasmids containing the acrAB (A) and acrEF (B) regions. Open arrows indicate the directions and extents of the acrA, acrB, acrS, acrE, and acrF genes. Arrowheads indicate the positions and directions of extension of the primers. Dotted bars represent the DNA fragments inserted into low-copy-number vectors, and a solid bar represents the DNA fragments inserted into a high-copy-number vector. Arrows indicate the direction of the lac promoter in the vectors.