Plasmid D, a hybrid of plasmids P- and R119, mediates polarized chromosome mobilization from one origin in strain PM5006, while the parental plasmids neither individually nor combined mobilize this chromosome. To elucidate its acquired mobilizing ability plasmid D was characterized physically in relation to P- and R119. Restriction patterns of these plasmids were compared and it was shown that D consists of P- and only the r-determinant (r-det) of R119. A mechanism for the formation of plasmid D, via transduction of the r-det and subsequent transposon-like integration into P-, involving insertion sequence IS1, was suggested. Evidence for aberration in plasmid D DNA as a result of r-det integration into P- was attributed to IS1 elements which flank the r-det. Recombination regions of parental plasmid DNA were located on dIII fragments α and β of plasmid D and were subsequently inserted into IncP-1 plasmid RP4 that fails to mobilize the chromosome. RP4:: dIII α plasmids did not mobilize the latter chromosome, but rendered the lac. RP4:: dIII β plasmids pMC1 and pMC17, containing the fragment in opposite orientations, mobilized the chromosome. For pMC17, mobilization was indistinguishable from that of plasmid D, i.e. having the same orientation and the same single origin. However, mobilization promoted by pMC1 was from two distinctly different origins, different from that of pMC17. This apparently deviates from known examples where inversion of homologous DNA inserted into plasmids leads to mobilization from the same origin but in reverse direction.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error