Recombinational repair of chromosomal DNA double‐strand breaks generated by a restriction endonuclease

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Abstract
DNA double‐strand break repair can be accomplished by homologous recombination when a sister chromatid or a homologous chromosome is available. However, the study of sister chromatid double‐strand break repair in prokaryotes is complicated by the difficulty in targeting a break to only one copy of two essentially identical DNA sequences. We have developed a system using the Escherichia coli chromosome and the restriction enzyme EcoKI, in which double‐strand breaks can be introduced into only one sister chromatid. We have shown that the components of the RecBCD and RecFOR ‘pathways’ are required for the recombinational repair of these breaks. Furthermore, we have shown a requirement for SbcCD, the prokaryotic homologue of Rad50/Mre11. This is the first demonstration that, like Rad50/Mre11, SbcCD is required for recombination in a wild‐type cell. Our work suggests that the SbcCD–Rad50/Mre11 family of proteins, which have two globular domains separated by a long coiled‐coil linker, is specifically required for the co‐ordination of double‐strand break repair reactions in which two DNA ends are required to recombine at one target site.