Genetic and physical studies of recombinant plasmids formed between an R plasmid of compatibility group FI and sex factor F of HfrH.

Recombinant plasmids between an R plasmid of the FI group (R162/3) and the sex factor F or HfrH were produced after the conjugal transfer of this R plasmid into HfrH. Three types of recombinant plasmids were identified after the mating of HfrH (R162/3) with recA and rec+ recipients. One specimen of each type (pIP218, pIP222, pIP226) was studied in this report. All three recombinant plasmids carry the same genetic information for resistance to antibiotics (CSSuT) retained from R162/3. pIP218 retained all the other properties from F of HfrH: derepression for pilus synthesis, mobilization of the chromosome for the proximally transferred HfrH genes (thr, leu, proA), interference with T7 propagation, and ability to be cured by acridine orange. pIP222 retained from F of HfrH the derepression for pilus synthesis and the same polarity of chromosome transfer (thr, leu, proA), while pIP226 retained the interference with T7 propagation and acridine orange curing. Physical studies revealed that replication control and/or recovery of F and pIP218 as covalent circles of deoxyribonucleic acid are similar, and are different from R162/3. The new plasmids are more likely the result of a substitutive recombination event than a fusion. We propose genetic maps of these recombinant plasmids, showing the unequal participation of the parental plasmids in their formation.