Genes of de novo pyrimidine biosynthesis from the hyperthermoacidophilic crenarchaeote Sulfolobus acidocaldarius: novel organization in a bipolar operon

Early Divergence and Gene Exchange Highways in the Evolutionary History of Mesoaciditogales

The placement of a nonhyperthermophilic order Mesoaciditogales as the earliest branching clade within the Thermotogota phylum challenges the prevailing hypothesis that the last common ancestor of Thermotogota was a hyperthermophile. Yet, given the long branch leading to the only two Mesoaciditogales described to date, the phylogenetic position of the order may be due to the long branch attraction artifact. By testing various models and applying data recoding in phylogenetic reconstructions, we observed that early branching of Mesoaciditogales within Thermotogota is strongly supported by the conserved marker genes assumed to be vertically inherited. However, based on the taxonomic content of 1,181 gene families and a phylogenetic analysis of 721 gene family trees, we also found that a substantial number of Mesoaciditogales genes are more closely related to species from the order Petrotogales. These genes contribute to coenzyme transport and metabolism, fatty acid biosynthesis, genes known to respond to heat and cold stressors, and include many genes of unknown functions. The Petrotogales comprise moderately thermophilic and mesophilic species with similar temperature tolerances to that of Mesoaciditogales. Our findings hint at extensive horizontal gene transfer (HGT) between, or parallel independent gene gains by, the two ecologically similar lineages and suggest that the exchanged genes may be important for adaptation to comparable temperature niches.

Antiviral and Antimicrobial Nucleoside Derivatives: Structural Features and Mechanisms of Action

The emergence of new viruses and resistant strains of pathogenic microorganisms has become a powerful stimulus in the search for new drugs. Nucleosides are a promising class of natural compounds, and more than a hundred drugs have already been created based on them, including antiviral, antibacterial and antitumor agents. The review considers the structural and functional features and mechanisms of action of known nucleoside analogs with antiviral, antibacterial or antiprotozoal activity. Particular attention is paid to the mechanisms that determine the antiviral effect of nucleoside analogs containing hydrophobic fragments. Depending on the structure and position of the hydrophobic substituent, such nucleosides can either block the process of penetration of viruses into cells or inhibit the stage of genome replication. The mechanisms of inhibition of viral enzymes by compounds of nucleoside and non-nucleoside nature have been compared. The stages of creation of antiparasitic drugs, which are based on the peculiarities of metabolic transformations of nucleosides in humans body and parasites, have been considered. A new approach to the creation of drugs is described, based on the use of prodrugs of modified nucleosides, which, as a result of metabolic processes, are converted into an effective drug directly in the target organ or tissue. This strategy makes it possible to reduce the general toxicity of the drug to humans and to increase the effectiveness of its action on cells infected by the virus.

Development of a genetic system for a model manganese-oxidizing proteobacterium, Leptothrix discophora SS1

Understanding the molecular underpinnings of manganese oxidation in Leptothrix discophora SS1 has been hampered by the lack of a genetic system. In this report, we describe the development of a genetic system for L. discophora SS1. The antibiotic sensitivity was characterized, and a procedure for transformation with exogenous DNA via conjugation was developed and optimized, resulting in a maximum transfer frequency of 5.2×10−1 and a typical transfer frequency of the order of 1×10−3 transconjugants per donor. Genetic manipulation of L. discophora SS1 was demonstrated by disrupting pyrF via chromosomal integration with a plasmid containing a R6Kγ origin of replication through homologous recombination. This resulted in resistance to 5-fluoroorotidine, which was abolished by complementation with an ectopically expressed copy of pyrF cloned into pBBR1MCS. This system is expected to be amenable to a systematic genetic analysis of L. discophora SS1, including those genes responsible for manganese oxidation.

Sa-Lrp from Sulfolobus acidocaldarius is a versatile, glutamine-responsive, and architectural transcriptional regulator

Sa-Lrp is a member of the leucine-responsive regulatory protein (Lrp)-like family of transcriptional regulators in Sulfolobus acidocaldarius. Previously, we demonstrated the binding of Sa-Lrp to the control region of its own gene in vitro. However, the function and cofactor of Sa-Lrp remained an enigma. In this work, we demonstrate that glutamine is the cofactor of Sa-Lrp by inducing the formation of octamers and increasing the DNA-binding affinity and sequence specificity. In vitro protein-DNA interaction assays indicate that Sa-Lrp binds to promoter regions of genes with a variety of functions including ammonia assimilation, transcriptional control, and UV-induced pili synthesis. DNA binding occurs with a specific affinity for AT-rich binding sites, and the protein induces DNA bending and wrapping upon binding, indicating an architectural role of the regulator. Furthermore, by analyzing an Sa-lrp deletion mutant, we demonstrate that the protein affects transcription of some of the genes of which the promoter region is targeted and that it is an important determinant of the cellular aggregation phenotype. Taking all these results into account, we conclude that Sa-Lrp is a glutamine-responsive global transcriptional regulator with an additional architectural role.

Mutation and reversion frequencies of different Sulfolobus species and strains

We have determined the apparent and actual spontaneous mutation frequencies and rates for different species and strains of the thermoacidophilic crenarchaeote Sulfolobus. The proportion of mutations caused by insertion sequences has also been analyzed. Mutation frequencies for S. islandicus (0.08-0.6 mutations per cell division and 10(7) cells) were below those determined for S. solfataricus and comparable to or lower than those for S. acidocaldarius. The proportion of insertion sequence mutations for the S. islandicus strains REN1H1 (9 out of 230) and HVE10/4 (0 out of 24) was found to be considerably lower than in S. solfataricus P1 and P2 and also low in comparison to other S. islandicus strains. Mutants defective in either the pyrEF genes or the lacS gene have been isolated. Their growth phenotype on selective and non-selective medium was examined and the inactivating mutations in either of the genes were determined. In addition the reversion frequencies for these mutants were measured and found to be in the range of <0.6-1.5 mutations per cell division and 10(8) cells. However, when being subjected to electroporation as a transformation procedure, increased reversion was observed.

An active nonautonomous mobile element in Sulfolobus islandicus REN1H1

In the crenarchaeote Sulfolobus islandicus REN1H1, a mobile element of 321 bp length has been shown to be active. It does not contain terminal inverted repeats and transposes by a replicative mechanism. This newly discovered element has been named SMN1 (for Sulfolobus miniature noninverted repeat transposable element).

Equal rates of repair of DNA photoproducts in transcribed and non-transcribed strands in Sulfolobus solfataricus

The nucleotide excision repair (NER) pathway removes bulky lesions such as photoproducts from DNA. In both bacteria and eukarya, lesions located in transcribed strands are repaired significantly faster than those located in non-transcribed strands due to damage signalling by stalled RNA polymerase molecules: a phenomenon known as transcription-coupled repair (TCR). TCR requires a mechanism for coupling the detection of stalled RNA polymerase molecules to the NER pathway, provided in bacteria by the Mfd protein. In the third domain of life, archaea, the pathway of NER is not well defined, there are no Mfd homologues and the existence of TCR has not been investigated. In this report we looked at rates of removal of photoproducts in three different operons of the crenarchaeon Sulfolobus solfataricus following UV irradiation. We found no evidence for significantly faster repair in the transcribed strands of these three operons. The rate of global genome repair in S. solfataricus is relatively rapid, and this may obviate the requirement for a specialized TCR pathway. Significantly faster repair kinetics were observed in the presence of visible light, consistent with the presence of a gene for photolyase in the genome of S. solfataricus.

Homologous recombination of exogenous DNA with the Sulfolobus acidocaldarius genome: properties and uses

In order to quantify recombination between exogenous DNA and the Sulfolobus acidocaldarius chromosome, we electroporated pyrE (uracil-auxtotrophic) recipient strains with functional pyrE sequences and counted Pyr+ transformants by direct plating. Certain culture and post-electroporation conditions increased the yield of Pyr+ recombinants from non-replicating pyrE plasmid, whereas cognate methylation of SuaI restriction sites in the plasmid decreased it. Recombination of linear DNAs with the S. acidocaldarius genome was proportional to the length of a limiting overlap, but even synthetic oligonucleotides produced reasonable numbers of recombinants with appropriate recipient strains. To investigate uses of this latter property, we electroporated an 18-bp pyrE deletion mutant with mixtures of synthetic oligonucleotides altering glycine-55 of the orotate phosphoribosyl transferase encoded by pyrE. Pyr+ transformants were recovered in which this codon was converted to each of the alternatives encoded by the oligonucleotide mixtures, thereby identifying five amino acid substitutions tolerated at this position of the thermostable enzyme.

The genome of Sulfolobus acidocaldarius, a model organism of the Crenarchaeota

Sulfolobus acidocaldarius is an aerobic thermoacidophilic crenarchaeon which grows optimally at 80 degrees C and pH 2 in terrestrial solfataric springs. Here, we describe the genome sequence of strain DSM639, which has been used for many seminal studies on archaeal and crenarchaeal biology. The circular genome carries 2,225,959 bp (37% G+C) with 2,292 predicted protein-encoding genes. Many of the smaller genes were identified for the first time on the basis of comparison of three Sulfolobus genome sequences. Of the protein-coding genes, 305 are exclusive to S. acidocaldarius and 866 are specific to the Sulfolobus genus. Moreover, 82 genes for untranslated RNAs were identified and annotated. Owing to the probable absence of active autonomous and nonautonomous mobile elements, the genome stability and organization of S. acidocaldarius differ radically from those of Sulfolobus solfataricus and Sulfolobus tokodaii. The S. acidocaldarius genome contains an integrated, and probably encaptured, pARN-type conjugative plasmid which may facilitate intercellular chromosomal gene exchange in S. acidocaldarius. Moreover, it contains genes for a characteristic restriction modification system, a UV damage excision repair system, thermopsin, and an aromatic ring dioxygenase, all of which are absent from genomes of other Sulfolobus species. However, it lacks genes for some of their sugar transporters, consistent with it growing on a more limited range of carbon sources. These results, together with the many newly identified protein-coding genes for Sulfolobus, are incorporated into a public Sulfolobus database which can be accessed at http://dac.molbio.ku.dk/dbs/Sulfolobus.

New insertion sequences of Sulfolobus: functional properties and implications for genome evolution in hyperthermophilic archaea

Analyses of complete genomes indicate that insertion sequences (ISs) are abundant and widespread in hyperthermophilic archaea, but few experimental studies have measured their activities in these hosts. As a way to investigate the impact of ISs on Sulfolobus genomes, we identified seven transpositionally active ISs in a widely distributed Sulfolobus species, and measured their functional properties. Six of the seven were found to be distinct from previously described ISs of Sulfolobus, and one of the six could not be assigned to any known IS family. A type II 'Miniature Inverted-repeat Transposable Element' (MITE) related to one of the ISs was also recovered. Rates of transposition of the different ISs into the pyrEF region of their host strains varied over a 250-fold range. The Sulfolobus ISs also differed with respect to target-site selectivity, although several shared an apparent preference for the pyrEF promoter region. Despite the number of distinct ISs assayed and their molecular diversity, only one demonstrated precise excision from the chromosomal target region. The fact that this IS is the only one lacking inverted repeats and target-site duplication suggests that the observed precise excision may be promoted by the IS itself. Sequence searches revealed previously unidentified partial copies of the newly identified ISs in the Sulfolobus tokodaii and Sulfolobus solfataricus genomes. The structures of these fragmentary copies suggest several distinct molecular mechanisms which, in the absence of precise excision, inactivate ISs and gradually eliminate the defective copies from Sulfolobus genomes.

Compositional nonrandomness upstream of start codons in archaebacteria

Since the regions directing transcriptional and translational initiation in archaebacteria are poorly characterized, the purpose of this study was to characterize them using measurements of nonrandomness upstream of start codons on eight fully sequenced archaebacterial genomes. Two distinctly different regions with conservation were identified. The location of the first corresponded well to the classical Shine-Dalgarno region (phi peak), and the other was located approximately 20-35 nucleotides upstream of start codons (alpha region), but both regions are not present in all strains. The composition of the region around the phi peak showed an overrepresentation of guanine, whereas composition in the alpha region had an overrepresentation of adenine and thymine. It is furthermore shown that the alpha region surprisingly is associated with start codon usage and other characteristics of the genes. The alpha region is likely to correspond to TATA-boxes and thereby indicates use of leaderless (or short-leadered) transcripts.

Molecular characteristics of spontaneous deletions in the hyperthermophilic archaeon Sulfolobus acidocaldarius

Prokaryotic genomes acquire and eliminate blocks of DNA sequence by lateral gene transfer and spontaneous deletion, respectively. The basic parameters of spontaneous deletion, which are expected to influence the course of genome evolution, have not been determined for any hyperthermophilic archaeon. We therefore screened a number of independent pyrimidine auxotrophs of Sulfolobus acidocaldarius for deletions and sequenced those detected. Deletions accounted for only 0.4% of spontaneous pyrE mutations, corresponding to a frequency of about 10(-8) per cell. Nucleotide sequence analysis of five independent deletions showed no significant association of the endpoints with short direct repeats, despite the fact that several such repeats occur within the pyrE gene and that duplication mutations in pyrE reverted at high frequencies. Endpoints of the spontaneous deletions did not coincide with short inverted repeats or potential stem-loop structures. No consensus sequence common to all the deletions could be identified, although two deletions showed the potential of being stabilized by octanucleotide sequences elsewhere in pyrE, and another pair of deletions shared an octanucleotide at their 3' ends. The unusually low frequency and low sequence dependence of spontaneous deletions in the S. acidocaldarius pyrE gene compared to other genetic systems could not be explained in terms of possible constraints imposed by the 5-fluoroorotate selection.

Construction of a shuttle vector for, and spheroplast transformation of, the hyperthermophilic archaeon Pyrococcus abyssi

Our understanding of the genetics of species of the best-studied hyperthermophilic archaea, Pyrococcus spp., is presently limited by the lack of suitable genetic tools, such as a stable cloning vector and the ability to select individual transformants on plates. Here we describe the development of a reliable host-vector system for the hyperthermophilic archaeon Pyrococcus abyssi. Shuttle vectors were constructed based on the endogenous plasmid pGT5 from P. abyssi strain GE5 and the bacterial vector pLitmus38. As no antibiotic resistance marker is currently available for Pyrococcus spp., we generated a selectable auxotrophic marker. Uracil auxotrophs resistant to 5-fluoorotic acid were isolated from P. abyssi strain GE9 (devoid of pGT5). Genetic analysis of these mutants revealed mutations in the pyrE and/or pyrF genes, encoding key enzymes of the pyrimidine biosynthetic pathway. Two pyrE mutants exhibiting low reversion rates were retained for complementation experiments. For that purpose, the pyrE gene, encoding orotate phosphoribosyltransferase (OPRTase) of the thermoacidophilic crenarchaeote Sulfolobus acidocaldarius, was introduced into the pGT5-based vector, giving rise to pYS2. With a polyethylene glycol-spheroplast method, we could reproducibly transform P. abyssi GE9 pyrE mutants to prototrophy, though with low frequency (10(2) to 10(3) transformants per micro g of pYS2 plasmid DNA). Transformants did grow as well as the wild type on minimal medium without uracil and showed comparable OPRTase activity. Vector pYS2 proved to be very stable and was maintained at high copy number under selective conditions in both Escherichia coli and P. abyssi.

High resolution contact probing of the Lrp-like DNA-binding protein Ss-Lrp from the hyperthermoacidophilic crenarchaeote Sulfolobus solfataricus P2

Ss-Lrp, from Sulfolobus solfataricus, is an archaeal homologue of the global bacterial regulator Lrp (Leucine-responsive regulatory protein), which out of all genome-encoded proteins is most similar to Escherichia coli Lrp (E-value of 5.6 e-14). The recombinant protein has been purified as a 68 kDa homotetramer. The specific binding of Ss-Lrp to its own control region is suggestive of negative autoregulation. A high resolution contact map of Ss-Lrp binding was established by DNase I and hydroxyl radical footprinting, small non-intercalating groove-specific ligand-binding interference, and various base-specific premodification and base removal binding interference techniques. We show that Ss-Lrp binds one face of the DNA helix and establishes the most salient contacts with two major groove segments and the intervening minor groove, in a region that overlaps the TATA-box and BRE promoter elements. Therefore, Ss-Lrp most likely exerts autoregulation by preventing promoter recognition by TBP and TFB. Moreover, the results demonstrate profound Ss-Lrp induced structural alterations of sequence stretches flanking the core contact site, and reveal that the deformability of these regions significantly contributes to binding selectivity.