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Isolation of genetic elements that increase frequencies of plasmid recombinants


Some plasmid DNAs, when maintained in wild-type Escherichia coli strains, form high levels of oligomeric species while others remain primarily monomers1–9. One explanation of this observation is that the plasmids that do not form circular oligomers lack a DNA sequence necessary for the formation or maintenance of circular oligomeric species. Here we describe the isolation of segments of DNA from the E. coli genome and other sources that through a recA+-dependent process: (1) stimulate the conversion of monomeric plasmids to different oligomeric forms, (2) stimulate the conversion of an oligomeric plasmid to a mixture of monomeric and different oligomeric forms, and (3) increase the frequency of recovery of figure-8 molecules. Both cis-acting and trans-acting elements were found. These elements seem to act by stimulating either the frequency of the recombination events that lead to the interconversion of different oligomeric plasmid DNA molecules or some process involved in the maintenance of newly-formed recombinant molecules.

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James, A., Morrison, P. & Kolodner, R. Isolation of genetic elements that increase frequencies of plasmid recombinants. Nature 303, 256–259 (1983).

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