New insights into NHEJ repair processes in prokaryotes

In eukaryotic cells, the repair of DNA double strand breaks (DSBs) by the non-homologous end-joining (NHEJ) pathway is critical for genome stability. Until recently it was assumed that this DSB repair pathway was restricted to the eukarya. However, a functionally homologous prokaryotic NHEJ repair apparatus has now been identified and characterised. In contrast to the complex eukaryotic system, bacterial NHEJ appears to require only two proteins, Ku and a multifunctional DNA ligase, which form a two-component repair complex at the termini of DSBs. Together, these DNA repair factors possess all of the break-recognition, end-processing and ligation activities required to facilitate the complex task of DSB repair, both in vitro and in vivo. Our recent findings lay the foundation for understanding the molecular mechanisms that co-ordinate the processing and joining of DSBs by NHEJ in bacteria and also provides a conceptual framework for delineating the end-processing reactions in eukaryotes.