Recombination genes on the Escherichia coli sex factor specific for transposable elements.

Abstract
The E. coli sex factor stimulates precise excision of transposons Tn5 and Tn10 from sites either within the bacterial chromosome or within the factor itself. Two kinds of mutations that affect this activity were isolated. The ferA mutations eliminate the stimulation; the ferB mutations enhance it in the presence of ferA+. Apparently, ferA defines a sex factor gene that stimulates precise excision. The ferB mutations also specifically increase the rate of recombination between 2 IS3 [insertion sequence] elements on F'' lac-pro (F''128) in a reaction that requires the product of recA. The stimulation of this recombination by ferB also requires an active ferA gene, which implies that the ferA gene stimulates this reaction and precise excision. A ferA mutation was mapped at 84.2 kilobases [kb] on the F factor, and a ferB mutation was mapped at 82.5 kb. The fer mutants were obtained by an approach that permits the isolation of mutants affecting precise excision.