Mobilization of the escherichia coli plasmid colEl (colicin E1) and colel vectors used in recombinant DNA experiments

The Escherichia coli ColE1 plasmid, which codes for production of colicin E1, is inherently nontransferable (nonconjugative) by bacterial mating. ColE1 can be transmitted at mating by a process called mobilization if ColE1 is coresident with a transfer plasmid. Mobilization is governed in part by a ColE1 gene called mob. ColE1 is mob+. Several ColE1 derivatives employed in recombinant DNA experiments, notably pBR313 and pBR322, are mob-. These cloning vehicles are mobilized at a markedly reduced frequency relative to ColE1. E. coli K12 carrying either pBR313 or pBR322 represents a useful host vector system for recombinant DNA experiments and affords a significant degree of biological containment.