Characterization of a translocation unit encoding resistance to mercuric ions that occurs on a nonconjugative plasmid in Pseudomonas aeruginosa

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Abstract
The nonconjugative plasmid pVS1 has a MW of 18.5 .times. 106 and confers resistance to sulfonamides and to Hg2+. In P. aeruginosa PAO, the transfer can be mobilized by a variety of conjugative plasmids, and the process does not require a functional recombination system in the donor. Hybrid plasmids that arise by the relocation of the mer gene onto the mobilizing plasmid can be isolated readily, and as far as can be determined, these hybrids retain the genome of the conjugative plasmid in toto. The relocation of mer occurs by a Rec-independent process and leads to a constant increase (.apprx. 6 .times. 106 daltons) in the size of the recipient plasmid. This suggests that the mer gene in pVS1 is located on a translocation unit, designated Tn501, of a MW of .apprx. 6 .times. 106. The translocation of Tn501 into RP1 is not usually associated with the loss of any known plasmid-mediated function, but transfer-defective or tetracycline-sensitive derivatives do occur at frequencies of .apprx. 4%, but carbenicillin-sensitive or kanamycin-sensitive variants arise with a frequency of .apprx. 0.2% each. The integration of Tn501 can apparently occur at any 1 of a minimum of 5 sites in RP1.