The DNA of all living organisms is constantly damaged by a wide variety of endogenous and exogenous agents. Double-stranded DNA breaks are particularly toxic and under certain conditions a single break will result in cell death. To preserve genome integrity, double-stranded breaks are faithfully repaired via homologous recombination. Recombinational repair in prokaryotes is generally initiated by a class of enzymes known as helicase-nucleases. These enzymes bind tightly to broken duplex DNA ends and use ATP driven motors to unwind the DNA.