Analysis of plasmid pIP1203. A) Agarose-gel electrophoresis of EcoRV-digested plasmid DNA from representative Yersinia pestis strain 6/69 (1) and from streptomycin-resistant strain 16/95 (2). B) Pulsed-field gel electrophoresis of pIP1203 DNA extracted from Escherichia coli K802N transconjugant and digested by EcoRV (1), EcoRI+EcoRV (2), and EcoRI (3). The arrow indicates the extra large-size DNA fragment in strain 16/95. The size of the molecular weight markers in kilobases is indicated at the