Genetic organization of the broad-host-range IncP-1 plasmid R751.

We have identified regions encoding conjugal transfer, plasmid maintenance, and trimethoprim resistance on the IncP-1 plasmid R751 by complementation tests with cloned deoxyribonucleic acid fragments and self-replicating derivatives constructed in vitro. The genes for replication and transfer show a scattered organization similar to that previously determined for RK2, another IncP-1 plasmid. Derivatives of RK2 are able to complement R751 derivatives defective in these functions. Restriction enzyme cleavage sites in R751 deoxyribonucleic acid are clustered in regions of the plasmid physical map. Neither region is required for plasmid maintenance or transfer, although one determines resistance to trimethoprim. A similar clustering of cleavage sites is seen with RK2, which nevertheless has a very different restriction map.