A conserved hexanucleotide motif is important in UV-inducible promoters in Sulfolobus acidocaldarius

Characterization of promoters in archaeal genomes based on DNA structural parameters

The transcription machinery of archaea can be roughly classified as a simplified version of eukaryotic organisms. The basal transcription factor machinery binds to the TATA box found around 28 nucleotides upstream of the transcription start site; however, some transcription units lack a clear TATA box and still have TBP/TFB binding over them. This apparent absence of conserved sequences could be a consequence of sequence divergence associated with the upstream region, operon, and gene organization. Furthermore, earlier studies have found that a structural analysis gains more information compared with a simple sequence inspection. In this work, we evaluated and coded 3630 archaeal promoter sequences of three organisms, Haloferax volcanii, Thermococcus kodakarensis, and Sulfolobus solfataricus into DNA duplex stability, enthalpy, curvature, and bendability parameters. We also split our dataset into conserved TATA and degenerated TATA promoters to identify differences among these two classes of promoters. The structural analysis reveals variations in archaeal promoter architecture, that is, a distinctive signal is observed in the TFB, TBP, and TFE binding sites independently of these being TATA-conserved or TATA-degenerated. In addition, the promoter encountering method was validated with upstream regions of 13 other archaea, suggesting that there might be promoter sequences among them. Therefore, we suggest a novel method for locating promoters within the genome of archaea based on DNA energetic/structural features.

Phosphoproteomic Analysis Reveals Rio1-Related Protein Phosphorylation Changes in Response to UV Irradiation in Sulfolobus islandicus REY15A

DNA damage response (DDR) in eukaryotes is largely regulated by protein phosphorylation. In archaea, many proteins are phosphorylated, however, it is unclear how the cells respond to DNA damage through global protein phosphorylation. We previously found that Δrio1, a Rio1 kinase homolog deletion strain of Sulfolobus islandicus REY15A, was sensitive to UV irradiation. In this study, we showed that Δrio1 grew faster than the wild type. Quantitative phosphoproteomic analysis of the wild type and Δrio1, untreated and irradiated with UV irradiation, revealed 562 phosphorylated sites (with a Ser/Thr/Tyr ratio of 65.3%/23.8%/10.9%) of 333 proteins in total. The phosphorylation levels of 35 sites of 30 proteins changed with >1.3-fold in the wild type strain upon UV irradiation. Interestingly, more than half of the UV-induced changes in the wild type did not occur in the Δrio1 strain, which were mainly associated with proteins synthesis and turnover. In addition, a protein kinase and several transcriptional regulators were differentially phosphorylated after UV treatment, and some of the changes were dependent on Rio1. Finally, many proteins involved in various cellular metabolisms exhibited Riol-related and UV-independent phosphorylation changes. Our results suggest that Rio1 is involved in the regulation of protein recycling and signal transduction in response to UV irradiation, and plays regulatory roles in multiple cellular processes in S. islandicus.

A CRISPR-associated factor Csa3a regulates DNA damage repair in Crenarchaeon Sulfolobus islandicus

CRISPR−Cas system provides acquired immunity against invasive genetic elements in prokaryotes. In both bacteria and archaea, transcriptional factors play important roles in regulation of CRISPR adaptation and interference. In the model Crenarchaeon Sulfolobus islandicus, a CRISPR-associated factor Csa3a triggers CRISPR adaptation and activates CRISPR RNA transcription for the immunity. However, regulation of DNA repair systems for repairing the genomic DNA damages caused by the CRISPR self-immunity is less understood. Here, according to the transcriptome and reporter gene data, we found that deletion of the csa3a gene down-regulated the DNA damage response (DDR) genes, including the ups and ced genes. Furthermore, in vitro analyses demonstrated that Csa3a specifically bound the DDR gene promoters. Microscopic analysis showed that deletion of csa3a significantly inhibited DNA damage-induced cell aggregation. Moreover, the flow cytometry study and survival rate analysis revealed that the csa3a deletion strain was more sensitive to the DNA-damaging reagent. Importantly, CRISPR self-targeting and DNA transfer experiments revealed that Csa3a was involved in regulating Ups- and Ced-mediated repair of CRISPR-damaged host genomic DNA. These results explain the interplay between Csa3a functions in activating CRISPR adaptation and DNA repair systems, and expands our understanding of the lost link between CRISPR self-immunity and genome stability.

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

Several species of Sulfolobales have been used as model organisms in the study of response mechanisms to ultraviolet (UV) irradiation in hyperthermophilic crenarchaea. To date, the transcriptional responses of genes involved in the initiation of DNA replication, transcriptional regulation, protein phosphorylation, and hypothetical function have been observed in Sulfolobales species after UV irradiation. However, due to the absence of knockout experiments, the functions of these genes under in situ UV irradiation have not yet been demonstrated. In the present study, we constructed five gene knockout strains (cdc6-2, tfb3, rio1, and two genes encoding the hypothetical proteins, Saci_0951 and Saci_1302) of Sulfolobus acidocaldarius and examined their sensitivities to UV irradiation. The knockout strains exhibited significant sensitivities to UV-B irradiation, indicating that the five UV-regulated genes play an important role in responses to UV irradiation in vivo. Furthermore, Δcdc6-2, Δrio1, ΔSaci_0951, and Δtfb3 were sensitive to a wide variety of helix-distorting DNA lesions, including UV-induced DNA damage, an intra-strand crosslink, and bulky adducts. These results reveal that cdc6-2, tfb3, rio1, and Saci_0951 are play more important roles in broad responses to helix-distorting DNA damage than in specific responses to UV irradiation.

Effect of UV irradiation on Sulfolobus acidocaldarius and involvement of the general transcription factor TFB3 in the early UV response

Exposure to UV light can result in severe DNA damage. The alternative general transcription factor (GTF) TFB3 has been proposed to play a key role in the UV stress response in the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius. Reporter gene assays confirmed that tfb3 is upregulated 90–180 min after UV treatment. In vivo tagging and immunodetection of TFB3 confirmed the induced expression at 90 min. Analysis of a tfb3 insertion mutant showed that genes encoding proteins of the Ups pili and the Ced DNA importer are no longer induced in a tfb3 insertion mutant after UV treatment, which was confirmed by aggregation assays. Thus, TFB3 plays a crucial role in the activation of these genes. Genome wide transcriptome analysis allowed a differentiation between a TFB3-dependent and a TFB3-independent early UV response. The TFB3-dependent UV response is characterized by the early induction of TFB3, followed by TFB3-dependent expression of genes involved in e.g. Ups pili formation and the Ced DNA importer. Many genes were downregulated in the tfb3 insertion mutant confirming the hypothesis that TFB3 acts as an activator of transcription. The TFB3-independent UV response includes the repression of nucleotide metabolism, replication and cell cycle progression in order to allow DNA repair.

An Orc1/Cdc6 ortholog functions as a key regulator in the DNA damage response in Archaea

While bacteria and eukaryotes show distinct mechanisms of DNA damage response (DDR) regulation, investigation of ultraviolet (UV)-responsive expression in a few archaea did not yield any conclusive evidence for an archaeal DDR regulatory network. Nevertheless, expression of Orc1-2, an ortholog of the archaeal origin recognition complex 1/cell division control protein 6 (Orc1/Cdc6) superfamily proteins was strongly activated in Sulfolobus solfataricus and Sulfolobus acidocaldarius upon UV irradiation. Here, a series of experiments were conducted to investigate the possible functions of Orc1-2 in DNA damage repair in Sulfolobus islandicus. Study of DDR in Δorc1-2 revealed that Orc1-2 deficiency abolishes DNA damage-induced differential expression of a large number of genes and the mutant showed hypersensitivity to DNA damage treatment. Reporter gene and DNase I footprinting assays demonstrated that Orc1-2 interacts with a conserved hexanucleotide motif present in several DDR gene promoters and regulates their expression. Manipulation of orc1-2 expression by promoter substitution in this archaeon revealed that a high level of orc1-2 expression is essential but not sufficient to trigger DDR. Together, these results have placed Orc1-2 in the heart of the archaeal DDR regulation, and the resulting Orc1-2-centered regulatory circuit represents the first DDR network identified in Archaea, the third domain of life.

Sulfolobus acidocaldarius Transports Pentoses via a Carbohydrate Uptake Transporter 2 (CUT2)-Type ABC Transporter and Metabolizes Them through the Aldolase-Independent Weimberg Pathway

Sulfolobus spp. possess a great metabolic versatility and grow heterotrophically on various carbon sources, such as different sugars and peptides. Known sugar transporters in Archaea predominantly belong to ABC transport systems. Although several ABC transporters for sugar uptake have been characterized in the crenarchaeon Sulfolobus solfataricus, only one homologue of these transporters, the maltose/maltooligomer transporter, could be identified in the closely related Sulfolobus acidocaldarius Comparison of the transcriptome of S. acidocaldarius MW001 grown on peptides alone and peptides in the presence of d-xylose allowed for the identification of the ABC transporter for d-xylose and l-arabinose transport and the gaining of deeper insights into pentose catabolism under the respective growth conditions. The d-xylose/l-arabinose substrate binding protein (SBP) (Saci_2122) of the ABC transporter is unique in Archaea and shares more similarity to bacterial SBPs of the carbohydrate uptake transporter-2 (CUT2) family than to any characterized archaeal one. The identified pentose transporter is the first CUT2 family ABC transporter analyzed in the domain of Archaea Single-gene deletion mutants of the ABC transporter subunits exemplified the importance of the transport system for d-xylose and l-arabinose uptake. Next to the transporter operon, enzymes of the aldolase-independent pentose catabolism branch were found to be upregulated in N-Z-Amine and d-xylose medium. The α-ketoglutarate semialdehyde dehydrogenase (KGSADH; Saci_1938) seemed not to be essential for growth on pentoses. However, the deletion mutant of the 2-keto-3-deoxyarabinoate/xylonate dehydratase (KDXD [also known as KDAD]; Saci_1939) was no longer able to catabolize d-xylose or l-arabinose, suggesting the absence of the aldolase-dependent branch in S. acidocaldarius IMPORTANCE Thermoacidophilic microorganisms are emerging model organisms for biotechnological applications, as their optimal growth conditions resemble conditions used in certain biotechnologies such as industrial plant waste degradation. Because of its high genome stability, Sulfolobus acidocaldarius is especially suited as a platform organism for such applications. For use in (ligno)cellulose degradation, it was important to understand pentose uptake and metabolism in S. acidocaldarius This study revealed that only the aldolase-independent Weimberg pathway is required for growth of S. acidocaldarius MW001 on d-xylose and l-arabinose. Moreover, S. acidocaldarius employs a CUT2 ABC transporter for pentose uptake, which is more similar to bacterial than to archaeal ABC transporters. The identification of pentose-inducible promoters will expedite the metabolic engineering of S. acidocaldarius for its development into a platform organism for (ligno)cellulose degradation.