Participation of UV-regulated Genes in the Response to Helix-distorting DNA Damage in the Thermoacidophilic Crenarchaeon Sulfolobus acidocaldarius

The RioK1 network determines p53 activity at multiple levels

By responding to a host of adverse conditions, ranging from DNA damage to viral infection, transcription factor p53 supports genomic stability, cellular health, and survival. Not surprisingly, tumours across the cancer spectrum carry mutations in p53, misexpress the protein, or dysregulate its activity. Several signalling pathways, many of which comprise oncogenic proteins, converge upon p53 to control its stability and activity. We here present the conserved kinase/ATPase RioK1 as an upstream factor that determines p53 activity at the DNA, RNA, and protein levels. It achieves this task by integrating the regulatory events that act on p53 into a coherent response circuit. We will also discuss how RIOK1 overexpression represents an alternative mechanism for cancers to inactivate p53, and how targeting RioK1 could eradicate malignancies that are driven by a dysregulated RioK1-p53 network.

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 Δssb in the thermophilic crenarchaeon S. acidocaldarius. Notably, an increase (29-fold) in mutation rate and a defect in HR frequency was observed in Δssb, indicating that SSB was involved in mutation avoidance and HR in vivo. We characterized the sensitivities of Δssb, in parallel with putative SSB-interacting protein-encoding gene-deleted strains, to DNA-damaging agents. The results showed that not only Δssb but also Δalhr1 and ΔSaci_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.

Horizontal Gene Transfer in Archaea-From Mechanisms to Genome Evolution

Archaea remains the least-studied and least-characterized domain of life despite its significance not just to the ecology of our planet but also to the evolution of eukaryotes. It is therefore unsurprising that research into horizontal gene transfer (HGT) in archaea has lagged behind that of bacteria. Indeed, several archaeal lineages may owe their very existence to large-scale HGT events, and thus understanding both the molecular mechanisms and the evolutionary impact of HGT in archaea is highly important. Furthermore, some mechanisms of gene exchange, such as plasmids that transmit themselves via membrane vesicles and the formation of cytoplasmic bridges that allows transfer of both chromosomal and plasmid DNA, may be archaea specific. This review summarizes what we know about HGT in archaea, and the barriers that restrict it, highlighting exciting recent discoveries and pointing out opportunities for future research. Expected final online publication date for the Annual Review of Microbiology, Volume 76 is September 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

PolB1 Is Sufficient for DNA Replication and Repair Under Normal Growth Conditions in the Extremely Thermophilic Crenarchaeon Sulfolobus acidocaldarius

The thermophilic crenarchaeon Sulfolobus acidocaldarius has four DNA polymerases (DNAPs): PolB1, PolB2, PolB3, and Dbh (PolY). Previous in vitro studies suggested that PolB1 is the main replicative DNAP of Sulfolobales whereas PolB2 and Y-family polymerases Dpo4 (Saccharolobus solfataricus) or Dbh are involved in DNA repair and translesion DNA synthesis. On the other hand, there are various opinions about the role of PolB3, which remains to be clearly resolved. In order to examine the roles of the DNAPs of S. acidocaldarius through in vivo experiments, we constructed polB2, polB3, and dbh deletion strains and characterized their phenotypes. Efforts to construct a polB1 deletion strain were not successful; in contrast, it was possible to isolate triple gene-deletion strains lacking polB2, polB3, and dbh. The growth of these strains was nearly the same as that of the parent strains under normal growth conditions. The polB2, polB3, and dbh single-deletion strains were sensitive to some types of DNA-damaging treatments, but exhibited normal sensitivity to UV irradiation and several other damaging treatments. Overall, the genotype which exhibited the greatest sensitivity to the DNA-damaging treatments we tested was the ΔpolB2 ΔpolB3 combination, providing the first evidence of overlapping function for these two DNAPs in vivo. The results of our study strongly suggest that PolB1 is responsible for the DNA replication of both the leading and lagging strands and is sufficient to complete the repair of most DNA damage under normal growth conditions in S. acidocaldarius.