Properties of hybrid plasmids, consisting of parts of the mini-R1 factorRsc11 andColE1

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Abstract
In vitro joining of the two small multicopy plasmidsRsc11 andColE1 by a poly dAdT linker resulted in hybrid plasmids, which determine resistance to ampicillin and immunity to colicin E1. Isolation of the plasmid DNA from single colonies revealed that a variety of hybrid plasmids was formed. Cleavage of these plasmids with restriction endonucleasesHincII,HindIII,EcoR1,SmaI andBamI and hybridization withColE1 demonstrated that they contain different parts of the parent plasmids,Rsc11 andColE1. Their copy number in the cell is between 6 and 15 per chromosome depending on the plasmid. None of these plasmids can replicate inpolA mutants. Replication continues in the presence of chloramphenicol. This suggests that replication can only occur from theColE1 origin and that the replication function of theRsc11 part is lost. The hybrid plasmids are compatible withRsc11 but not withColE1. The comparison of the physical maps of theseRsc11-ColE1 hybrids with their functions allows a partial determination of the location of ampicillin resistance, replication and incompatibility on theRsc11 genome.