Excision of F plasmid sequences by recombination at directly repeated insertion sequence 2 elements: involvement of recA.

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Abstract
The DNA of the F plasmid is joined to bacterial [Escherichia coli] DNA sequences in the F'' ORF203 by directly repeated insertion sequence 2 (IS2) elements. The rate of excision of the F plasmid from this F'' (presumably by recombination at the directly repeated IS2) was estimated in recA+ and recA- strains. Normal F is produced in the recA+ strain, but is not detected in recA-. The autonomous plasmids produced in the recA- background were F'' having deletions. F excision in this particular recA+ case is specific in the sense that the directly repeated IS2 appear to be more active in recombination than simialr disposed IS3 direct repetitions in this F''.