Substrate specificity and action mechanism of the HerA-NurA nuclease from the hyperthermophilic archaeon <i>Thermococcus kodakarensis</i>

To understand the specific function of the HerA-NurA complex, which is believed to function in the end resection process to create a 3'-overhanging DNA for the following strand invasion in homologous recombination, we performed biochemical and structural analyses of this complex from a hyperthermophilic archaeon, <i>Thermococcus kodakarensis</i>, inhabiting a harsh environment where DNA is easily damaged. We found that the HerA-NurA complex cleaves both strands of double-stranded DNA in an exonucleolytic manner, regardless of the structure of the DNA end. Our structural analysis revealed the detailed characteristics of the nuclease activity exhibited by the HerA-NurA complex. Based on the presented information, it is unlikely that the HerA-NurA complex directly functions in end resection, but rather is involved in other functions, possibly in defense against viral infections.