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

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 Sulfolobus 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 Sulfolobus in vivo. Here, we characterized mutant phenotypes of the ssb-deleted strain Delta ssb in the thermophilic crenarchaeon S. acidocaldarius. Notably, an increase (29-fold) in mutation rate and a defect in HR frequency was observed in Delta ssb, indicating that SSB was involved in mutation avoidance and HR in vivo. We characterized the sensitivities of Delta ssb, in parallel with putative SSB-interacting protein-encoding gene-deleted strains, to DNA-damaging agents. The results showed that not only Delta ssb but also Delta alhr1 and Delta Saci_0790 were markedly sensitive to a wide variety of helix-distorting DNA-damaging agents, indicating that SSB, a novel helicase SacaLhr1, 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.

Automated summary

The study of DNA repair in hyperthermophiles can uncover the mechanisms of genome integrity maintenance systems in extreme conditions. Previous studies have shown that the single-stranded DNA-binding protein (SSB) from Sulfolobus is involved in maintaining genome integrity, including mutation avoidance, homologous recombination, and repair of helix-distorting DNA lesions. In this study, the mutant phenotypes of the SSB-deleted strain Delta ssb in S. acidocaldarius were characterized, revealing an increase in mutation rate and a defect in homologous recombination. This study expands our understanding of the impact of SSB on genome integrity and identifies key proteins involved in repair mechanisms in hyperthermophilic archaea.