Chi-dependent formation of linear plasmid DNA in exonuclease-deficient recBCD+ strains of Escherichia coli.

Escherichia coli strains carrying mutations in sbcB (exonuclease I) or xthA (exonuclease III) accumulate high-molecular-weight linear plasmid concatemers when transformed with plasmids containing the chi sequence, 5'-GCTGGTGG-3'. Chi-dependent formation of high-molecular-weight plasmid DNA is dependent on recA and recF functions. In addition, chi stimulation occurs only in cis. Our data are consistent with models in which RecA and RecF proteins bind to and protect the DNA ends produced by RecBCD-chi interaction.