Figure 1 - Structure of the plasmid pVM3 and the location of mini-Mu insertions. A partial restriction map of the original plasmid pVM3 is shown with the recognition sites for relevant enzymes. The locations of the MudII1734 insertions (triangles) in plasmid pVM383, derived from pVM3 after removing a 7.2-kb ClaI-BstEII fragment, deduced from BamHI and HindIII digestion of the mutated plasmids, are also shown, since the P. mirabilis sequences were maintained in both plasmids. 1, pVM27; 2, pVM77; 3, pVM91. The HindIII recognition site at the left end of MudII1734 is shown to indicate the orientation of the insertions. Kanamycin (Km) and ampicillin (Ap) were used, when appropriate, at the concentrations of 50 µg/ml and 100 µg/ml, respectively. Transformation of E. coli cells by the CaCl2 method, plasmid isolation, DNA manipulation methods and gel electrophoresis were performed according to Sambrook et al. (15), where the media are also indicated. Digestion with restriction enzymes was performed as recommended by the manufacturer (GIBCO-BRL). Tc, Tetracycline.