Recombinational instability of F′ plasmids inEscherichia coliK-12

摘要

The F′ plasmids ORF-1 (purE+tsxsproC+lac+) and F′14 (agrE+metB+ilv+) contain active regions of recombination,freI andfreII correspondingly. The plasmid ORF-1 is stable inrecF−cells. (i.e., with the RecBC pathway of recombination) and decays inrec+cells (RecBCF pathway) giving two types of product: F+and plasmid pCK-1 (tsxsproC+lac+) containing part of the initial DNA. They are extremely instable in the presence of the RecF pathway, (recBC−sbcB−), yielding F+and plasmid pCK-2 (proC+lac+). The instability of plasmids depends on a region of homology between the chromosome and the episome. The instability of ORF-1 shows the participation of IS3 elements (α1β3and α3β1) in therecA, recF-dependent recombinational decay and allows localization of two active sites on the chromosome:freI1 betweenpurEandtsxmarkers andfreI2 betw