Response of the Hyperthermophilic ArchaeonSulfolobus solfataricusto UV Damage

Abstract

In order to characterize the genome-wide transcriptional response of the hyperthermophilic, aerobic crenarchaeote Sulfolobus solfataricus to UV damage, we used high-density DNA microarrays which covered 3,368 genetic features encoded on the host genome, as well as the genes of several extrachromosomal genetic elements. While no significant up-regulation of genes potentially involved in direct DNA damage reversal was observed, a specific transcriptional UV response involving 55 genes could be dissected. Although flow cytometry showed only modest perturbation of the cell cycle, strong modulation of the transcript levels of the Cdc6 replication initiator genes was observed. Up-regulation of an operon encoding Mre11 and Rad50 homologs pointed to induction of recombinational repair. Consistent with this, DNA double-strand breaks were observed between 2 and 8 h after UV treatment, possibly resulting from replication fork collapse at damaged DNA sites. The strong transcriptional induction of genes which potentially encode functions for pilus formation suggested that conjugational activity might lead to enhanced exchange of genetic material. In support of this, a statistical microscopic analysis demonstrated that large cell aggregates formed upon UV exposure. Together, this provided supporting evidence to a link between recombinational repair and conjugation events.Most organisms meet the challenge of maintaining their genome integrity and ensuring correct replication of their genetic material while protecting themselves against the DNAdamaging effects of UV light. This is reflected in the large number of proteins involved in DNA repair pathways, which are found in all three domains of life: Bacteria, Eukarya, and Archaea. For hyperthermophilic organisms, like many archaea, that dwell at the upper temperature limit of life (48), this challenge might be even more demanding. Studies on mutation frequencies and repair in Archaea have been inspired by the expectation that extremophiles growing under conditions which accelerate spontaneous DNA damage should be particularly proficient in DNA repair (7,14,32). Archaea have also gained special interest because of their unique evolutionary position and their relationship to eukaryotes. Homology in many factors in the systems responsible for transcription and replication has been observed. The homologous, yet simpler, archaeal systems provide a powerful tool for the study of cellular evolution and more complex systems in the eukaryotic nucleus (11). The homology between the eukaryotic and archaeal domains also exists in DNA repair systems (2, 23). For example, potential factors involved in nucleotide excision repair (NER) of UV-induced DNA lesions are, in most archaea, exclusively constituted by homologs of the eukaryotic proteins XPF/XPB/XPD/Fen-1. The in vivo function of this system in archaea has not yet been elucidated, and the system also seems to be incomplete (23, 39). However, Salerno et al. (42) have shown that Sulfolobus can efficiently conduct the repair of photoprodu...

Chromosome replication dynamics in the archaeon Sulfolobus acidocaldarius

“…5), whereas cells arrested by acetate showed elevated levels of Orc1-2 and low levels of Orc1-1 and Orc1-3 (1); resumption of growth after arrest resulted in elevated Orc1-1 and -3 and greatly reduced Orc1-2. Several laboratories have reported microarray analyses of the response of the Sulfolobus transcriptome to a range of physiological stresses such as UV treatment, viral infection, and heat shock (21)(22)(23)(24). Interestingly, these studies have revealed modulation of Orc1 gene transcript and/or protein levels; similar to that seen with microarray analysis of acetate-treated cells (25).…”

“…Volumetric cell count analysis was carried out within 10 min of dilution to avoid any cell volume changes that occurred after extended periods after dilution. For flow cytometry, cells were fixed with ice-cold ethanol (70% final concentration) and then prepared as described (21). Approximately 10 5 cells were analyzed to generate DNA content distributions by using a MoFlo cell sorter (Dako), as described (3).…”

Transcriptome Analysis of Infection of the Archaeon Sulfolobus solfataricus with Sulfolobus Turreted Icosahedral Virus

“…This is evident from a comparison of the response to infection by STIV with the induction of SSV1 by UV (3,4) and exposure of S. solfataricus to heat shock (28). When exposed to UV light to induce SSV1 production or heat shock, S. solfataricus regulates the transcription of several known stress response genes.…”

“…In response to UV exposure, transcription of genes encoding the three Sso7d proteins is down-regulated, as is the gene for a proteosome-associated nucleotidase (SSO0271). Of the 55 host genes identified as responding to UV exposure, 21 are shared with STIV infec-tion; however, genes down-regulated by UV tend to be upregulated by STIV infection (3). Heat shock of S. solfataricus results in a strong stress response with SSO271 down-regulated, but the genes for Sso7d proteins are up-regulated.…”

Massive Activation of Archaeal Defense Genes during Viral Infection

“…However, a pronounced increase of expression of IS elements of S. solfataricus has been observed as a result of heat shock and UV irradiation (38). Therefore, high expression of IS elements was suggested to be associated with the general stress response of S. solfataricus (36).…”