Properties of plasmids produced by recombination between R factors of groups J and FII

Recombinant plasmids have been produced both by transduction of genetic material from FIIR factors into Proteus mirabilis strains carrying plasmids of group J and by insertion of a transposon conferring streptomycin and trimethoprim resistances into a J group R factor. The transposon-carrying derivative and one of the transductants were shown to be members of group J whereas another transductant was shown to be compatible with members of this group. This recombinant plasmid was able to eliminate but not to be eliminable by R factors of group FII. A model for the origin of this anomalous compatibility characteristic is presented based on the assumption that the recombinant plasmid carries part but not all of a complex of binding sites for the repressor of replication [Uhlin and Nordström (1975)].