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Euryarchaea Okazaki fragments maturation components

DNA ligases join the ends of DNA molecules during replication, repair and recombination. ATP-dependent ligases are found predominantly in the eukarya and archaea whereas NAD+ -dependent DNA ligases are found only in the eubacteria and in entomopoxviruses. Using the genetically tractable halophile Haloferax volcanii as a model system, we described the first genetic analysis of archaeal DNA ligase function. We showed that the H. volcanii ATP-dependent DNA ligase family member, LigA, is non-essential for cell viability, raising the question of how DNA strands are joined in its absence. We show that H. volcanii also encodes an NAD+ -dependent DNA ligase family member, LigN, the first such enzyme to be identified in the archaea, and present phylogenetic analysis indicating that the gene encoding this protein has been acquired by lateral gene transfer (LGT) from eubacteria. As with LigA, we show that LigN is also non-essential for cell viability. Simultaneous inactivation of both proteins is lethal, however, indicating that they now share an essential function. Thus the LigN protein acquired by LGT appears to have been co-opted as a back-up for LigA function, perhaps to provide additional ligase activity under conditions of high genotoxic stress.

Reported by

University of Copenhagen
University of Copenhagen, Solgade 83 H
1307 Copenhagen