EcoRI restriction endonuclease map of the composite R plasmid NR1

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Abstract
A physical map of the composite R plasmid NR1 was constructed using specific cleavage of DNA by the restriction endonuclease EcoRI. Digestion of composite NR1 DNA by EcoRI yields 13 fragments. The 6 largest fragments (designated A-F) are from the resistance transfer factor component that harbors the tetracycline resistance genes (RTF-TC). The 7 smallest fragments (designated G-M) are from the r-determinants component that harbors the chloramphenicol (CM), streptomycin-spectinomycin (SM/SP) and sulfonamide (SA) resistance genes. The largest fragments of several RTF-TC segregants of NR1 that have deleted the r-determinants component is 0.8 .times. 106 daltons larger than fragment A of composite NR1. Only a part of fragment H of the r-determinants component is amplified in transitioned NR1 DNA in Proteus mirabilis, which consists of multiple, tandem sequences of r-determinants attached to a single copy of the RTF-TC component. Both of these changes can be explained by the locations of the excision sites at the RTF-TC: r-determinants junctions that are involved in the dissociation and reassociation of the RTF-TC and r-determinants components. The 13 fragments of composite NR1 DNA produced by EcoRI were ordered using partial digestion techniques. The order of the fragments is: .**GRAPHIC**. The approximate locations of the TC, CM, SM/SP and SA resistance genes on the EcoRI map were determined by analyzing several deletion mutants of NR1.