Resistance to UV Irradiation Caused by Inactivation of and Genes in Thermus thermophilus.

NurA and HerA are thought to be essential proteins for DNA end resection in archaeal homologous recombination systems. , an extremely thermophilic eubacterium, has proteins that exhibit significant sequence similarity to archaeal NurA and HerA. To unveil the cellular function of NurA and HerA in , we performed phenotypic analysis of disruptant mutants of and with or without DNA-damaging agents. The and genes were not essential for survival, and their deletion had no effect on cell growth and genome integrity. Unexpectedly, these disruptants of showed increased resistance to UV irradiation and mitomycin C treatment. Further, these disruptants and the wild type displayed no difference in sensitivity to oxidative stress and a DNA replication inhibitor. NurA had nuclease activity, and HerA had ATPase. The overexpression of loss-of-function mutants of and in the respective disruptants showed no complementation, suggesting their enzymatic activities were involved in the UV sensitivity. In addition, NurA and HerA interacted with each other and , forming a complex with 2:6 stoichiometry. These results suggest that the NurA-HerA complex has an architecture similar to that of archaeal counterparts but that it impairs, rather than promotes, the repair of photoproducts and DNA cross-links in cells. This cellular function is distinctly different from that of archaeal NurA and HerA. Many nucleases and helicases are engaged in homologous recombination-mediated DNA repair. Previous analyses in archaea indicated that NurA and HerA are the recombination-related nuclease and helicase. However, their cellular function had not been fully understood, especially in bacterial cells. In this study, we performed analyses to address the cellular function of and in an extremely thermophilic bacterium, As a result, NurA and HerA exhibited an interfering effect on the repair of several instances of DNA damage in the cell, which is in contrast to the results in archaea. This finding will facilitate our understanding of the diverse cellular functions of the recombination-related nucleases and helicases.