Construction of plasmid R6K derivatives in vitro: Characterization of the R6K replication region

Low molecular weight derivatives of the antibiotic resistance plasmid R6K have been constructed in vitro using the restriction endonucleases HindIII and HaeII. Common to all of the derivatives that replicate autonomously in Escherichia coli is a 2.1-kb segment of the DNA at the region of the origin of replication. This 2.1-kb region does not contain the asymmetric terminus of replication present in the parent plasmid. The derivatives replicate under relaxed control and are incompatible with intact R6K. A restriction endonuclease cleavage map of the plasmid is presented.