The Stabilization of Episomal Integration by Genetic Inversion: A General Hypothesis

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Abstract
In F' cells of Escherichia coli K12, recombination in the region of genetic duplication between chromosome and F-genote produces a rapid alteration between the integrated and detached states of the episome. Nevertheless, F' strains can give rise to Hfr cells in which the F-genote has undergone stable integration. We have found that one such Hfr has retained the genetic duplication as well as the recombination proficiency of the parental F' strain; to account for the failure of recombination to detach the episome in this Hfr, we have postulated the inversion of one of the duplicated regions. A general model is presented, showing that an inversion must prevent episome detachment by any combination of genetic crossovers.