Recombination between bacterial plasmids leading to the formation of plasmid multimers.

We report here the formation of plasmid multimers in E. coli. Multimers are covalently closed, circular molecules composed of tandem repeats of the monomer plasmid. Multimer formation occurs at high frequency in rec+, recB-C-, and recF- hosts. Multimer formation is not detected in recA- hosts and occurs at reduced frequency in recB-C-F- hosts. We conclude that multimer formation is mediated by a single reciprocal recombination event occurring at homologous regions on the two plasmids.