Resistance to UV Irradiation Caused by Inactivation ofnurAandherAGenes in Thermus thermophilus

Abstract

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.

Identification of general acid catalyst for the ATPase activity of Lynch syndrome-related MutL homologs

“…The mutL -lacking T. thermophilus HB8 strain was constructed as previously described (47). The wildtype, R27E, K78A, K78R, and K291A T. thermophilus mutL genes were ligated into the pMK18::HygΔKan plasmid (54,55) using XbaI and HindIII restriction sites. These plasmids were then transformed into the mutL -lacking T. thermophilus HB8 strain.…”

Take a Break to Repair: A Dip in the World of Double-Strand Break Repair Mechanisms Pointing the Gaze on Archaea

“…Moreover, two widely conserved archaeal genes, herA and nurA, have been implicated in HR since they are usually encoded in the same operon of Mre11 and Rad50 (Figure 9) [165][166][167] and the four genes are co-induced in response to UV irradiation [154,168]. Several studies have demonstrated that DNA resection requires the cooperation between the ATP-dependent Mre11-Rad50 and HerA-NurA complexes [169][170][171][172].…”

Haloferax volcanii —a model archaeon for studying DNA replication and repair

“…In thermophilic archaea, herA and nurA are encoded in the same operon as rad50 and mre11 [400]. HerA and NurA have been shown to interact with each other both in vitro and in vivo [401]. The HerA-NurA ATP-dependent helicase-nuclease complex cooperates with Rad50-Mre11 to coordinate the repair of DSBs, although the mechanism has not yet been described in detail [400,[402][403][404].…”

“…Genetic studies have shown this is not the case in bacterial species Deinococcus radiodurans and Thermus thermophilus [ 406 ]; in the latter, deletion of nurA and herA has no effect on cell growth. Unexpectedly, T. thermophilus cells lacking nurA and herA show increased resistance to UV irradiation and MMC treatment [ 401 ].…”