Comparative biology of two natural variants of the IncQ-2 family plasmids, pRAS3.1 and pRAS3.2.
Plasmids pRAS3.1 and pRAS3.2 are two closely related, natural variants of the IncQ-2 plasmid family that have identical plasmid backbones except for two differences. Plasmid pRAS3.1 has five 6-bp repeat sequences in the promoter region of the mobB gene and four 22-bp iterons in its oriV region, whereas pRAS3.2 has only four 6-bp repeats and three 22-bp iterons. Plasmid pRAS3.1 was found to have a higher copy number than pRAS3.2, and we show that the extra 6-bp repeat results in an increase in mobB and downstream mobA/repB expression. Placement of repB (primase) behind an arabinose-inducible promoter in trans resulted in an increase in repB expression and an approximately twofold increase in the copy number of plasmids with identical numbers of 22-bp iterons. The pRAS3 plasmids were shown to have a previously unrecognized toxin-antitoxin plasmid stability module within their replicons. The ability of the pRAS3 plasmids to mobilize the oriT regions of two other plasmids of the IncQ-2 family, pTF-FC2 and pTC-F14, suggested that the mobilization proteins pRAS3 are relaxed and can mobilize oriT regions with substantially different sequences. Plasmids pRAS3.1 and pRAS3.2 were highly incompatible with plasmids pTF-FC2 and pTC-F14, and this incompatibility was removed on inactivation of an open reading frame situated downstream of the mobCDE mobilization genes rather than being due to the 22-bp oriV-associated iterons. We propose that the pRAS3 plasmids represent a third, gamma incompatibility group within the IncQ-2 family plasmids.
Loftie-Eaton
Wesley
W
Department of Microbiology, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa.
Rawlings
Douglas E
DE
D048409:Aeromonas salmonicida / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D014644:Genetic Variation; D010802:Phylogeny; D010957:Plasmids / Q000145:classification*
D001426:Bacterial Proteins
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