The Impact of Single-Stranded DNA-Binding Protein SSB and Putative SSB-Interacting Proteins on Genome Integrity in the Thermophilic Crenarchaeon .

The study of DNA repair in hyperthermophiles has the potential to elucidate the mechanisms of genome integrity maintenance systems under extreme conditions. Previous biochemical studies have suggested that the single-stranded DNA-binding protein (SSB) from the hyperthermophilic crenarchaeon is involved in the maintenance of genome integrity, namely, in mutation avoidance, homologous recombination (HR), and the repair of helix-distorting DNA lesions. However, no genetic study has been reported that elucidates whether SSB actually maintains genome integrity in in vivo. Here, we characterized mutant phenotypes of the -deleted strain Δ in the thermophilic crenarchaeon . Notably, an increase (29-fold) in mutation rate and a defect in HR frequency was observed in Δ, indicating that SSB was involved in mutation avoidance and HR in vivo. We characterized the sensitivities of Δ, in parallel with putative SSB-interacting protein-encoding gene-deleted strains, to DNA-damaging agents. The results showed that not only Δ but also Δ and ΔSaci_0790 were markedly sensitive to a wide variety of helix-distorting DNA-damaging agents, indicating that SSB, a novel helicase aLhr1, and a hypothetical protein Saci_0790, were involved in the repair of helix-distorting DNA lesions. This study expands our knowledge of the impact of SSB on genome integrity and identifies novel and key proteins for genome integrity in hyperthermophilic archaea in vivo.