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Multiple Ku orthologues mediate DNA non‐homologous end‐joining in the free‐living form and during chronic infection of Sinorhizobium meliloti
Author(s) -
Kobayashi Hajime,
Simmons Lyle A.,
Yuan Daniel S.,
Broughton William J.,
Walker Graham C.
Publication year - 2008
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2007.06036.x
Subject(s) - biology , sinorhizobium meliloti , gene , homologous recombination , dna , non homologous end joining , dna repair , microbiology and biotechnology , homologous chromosome , bacteria , genetics , symbiosis
Summary The bacterial non‐homologous end‐joining (NHEJ) apparatus is a two‐component system that uses Ku and LigD to repair DNA double‐strand breaks. Although the reaction mechanism has been extensively studied, much less is known about the physiological role of bacterial NHEJ. Recent studies suggest that NHEJ acts under conditions where DNA replication is reduced or absent (such as in a spore or stationary phase). Interestingly, genes encoding Ku and LigD have been identified in a wide range of bacteria that can chronically infect eukaryotic hosts. Strikingly, Sinohizobium meliloti , an intracellular symbiont of legume plants, carries four genes encoding Ku homologues ( sku 1 to sku 4). Deletion analysis of the sku genes indicated that all Ku homologues are functional. One of these genes, sku 2, is strongly expressed in free‐living cells, as well as in bacteroid cells residing inside of the host plant. To visualize the NHEJ apparatus in vivo , SKu2 protein was fused to yellow fluorescent protein (YFP). Ionizing radiation (IR) induced focus formation of SKu2‐YFP in free‐living cells in a dosage‐dependent manner. Moreover, SKu2‐YFP foci formed in response to IR in non‐dividing bacteroids, indicating that NHEJ system is functional even during the chronic infection phase of symbiosis.