Sequences and replication of genomes of the archaeal rudiviruses SIRV1 and SIRV2: relationships to the archaeal lipothrixvirus SIFV and some eukaryal viruses. (1/10)

The double-stranded DNA genomes of the viruses SIRV1 and SIRV2, which infect the extremely thermophilic archaeon Sulfolobus and belong to the family Rudiviridae, were sequenced. They are linear, covalently closed at the ends, and 32,312 and 35,502 bp long, respectively, with an A+T content of 75%. The genomes of SIRV1 and SIRV2 carry inverted terminal repeats of 2029 and 1628 bp, respectively, which contain multiple direct repeats. SIRV1 and SIRV2 genomes contain 45 and 54 ORFs, respectively, of which 44 are homologous to one another. Their predicted functions include a DNA polymerase, a Holliday junction resolvase, and a dUTPase. The genomes consist of blocks with well-conserved sequences separated by nonconserved sequences. Recombination, gene duplication, horizontal gene transfer, and substitution of viral genes by homologous host genes have contributed to their evolution. The finding of head-to-head and tail-to-tail linked replicative intermediates suggests that the linear genomes replicate by the same mechanism as the similarly organized linear genomes of the eukaryal poxviruses, African swine fever virus and Chlorella viruses. SIRV1 and SIRV2 both contain motifs that resemble the binding sites for Holliday junction resolvases of eukaryal viruses and may use common mechanisms for resolution of replicative intermediates. The results suggest a common origin of the replication machineries of the archaeal rudiviruses and the above-mentioned eukaryal viruses. About 1/3 of the ORFs of each rudivirus have homologs in the Sulfolobus virus SIFV of the family Lipothrixviridae, indicating that the two viral families form a superfamily. The finding of inverted repeats of at least 0.8 kb at the termini of the linear genome of SIFV supports this inference.  (+info)

AFV1, a novel virus infecting hyperthermophilic archaea of the genus acidianus. (2/10)

We describe a novel virus, AFV1, of the hyperthermophilic archaeal genus Acidianus. Filamentous virions are covered with a lipid envelope and contain at least five different proteins with molecular masses in the range of 23-130 kDa and a 20.8-kb-long linear double-stranded DNA. The virus has been assigned to the family Lipothrixviridae on the basis of morphotypic characteristics. Host range is confined to several strains of Acidianus and the virus persists in its hosts in a stable carrier state. The latent period of virus infection is about 4 h. Viral DNA was sequenced and sequence similarities were found to the lipothrixvirus SIFV, the rudiviruses SIRV1 and SIRV2, as well as to conjugative plasmids and chromosomes of the genus Sulfolobus. Exceptionally for the linear genomes of archaeal viruses, many short direct repeats, with the sequence TTGTT or close variants thereof, are closely clustered over 300 bp at each end of the genome. They are reminiscent of the telomeric ends of linear eukaryal chromosomes.  (+info)

Structure and genome organization of AFV2, a novel archaeal lipothrixvirus with unusual terminal and core structures. (3/10)

A novel filamentous virus, AFV2, from the hyperthermophilic archaeal genus Acidianus shows structural similarity to lipothrixviruses but differs from them in its unusual terminal and core structures. The double-stranded DNA genome contains 31,787 bp and carries eight open reading frames homologous to those of other lipothrixviruses, a single tRNA(Lys) gene containing a 12-bp archaeal intron, and a 1,008-bp repeat-rich region near the center of the genome.  (+info)

Crystallization and preliminary X-ray diffraction analysis of protein 14 from Sulfolobus islandicus filamentous virus (SIFV). (4/10)

A large-scale programme has been embarked upon aiming towards the structural determination of conserved proteins from viruses infecting hyperthermophilic archaea. Here, the crystallization of protein 14 from the archaeal virus SIFV is reported. This protein, which contains 111 residues (MW 13 465 Da), was cloned and expressed in Escherichia coli with an N-terminal His(6) tag and purified to homogeneity. The tag was subsequently cleaved and the protein was crystallized using PEG 1000 or PEG 4000 as a precipitant. Large crystals were obtained of the native and the selenomethionine-labelled protein using sitting drops of 100-300 nl. Crystals belong to space group P6(2)22 or P6(4)22, with unit-cell parameters a = b = 68.1, c = 132.4 A. Diffraction data were collected to a maximum acceptable resolution of 2.95 and 3.20 A for the SeMet-labelled and native protein, respectively.  (+info)

Murine gammaherpesvirus 68 ORF20 induces cell-cycle arrest in G2 by inhibiting the Cdc2-cyclin B complex. (5/10)

The objective of this work was to identify novel viral 'evasion' genes without homology in the database through functional assays. Using this approach, the 'unassigned', conserved murine gammaherpesvirus ORF20 gene was shown to localize in the nucleus and to induce cell-cycle arrest followed by apoptosis in both mouse and human cells. Such growth-arrested cells did not express phospho-histone H3, demonstrating that the virus protein caused arrest at the G2 stage of the cell cycle. To characterize the mechanism further, Western blots of ORF20-recombinant lentivirus-infected cells were developed with antibodies to cyclin B1, Cdc2 and phospho-Tyr-15-Cdc2. This analysis revealed a relative increase in cyclin B and phospho-Tyr-15-Cdc2, from 24 to 72 h after infection with recombinant lentivirus. The demonstration that Cdc2 is in its inactive phosphorylated form and the clearly increased levels of cyclin B indicated that the virus gene blocks the progression of cells into mitosis by acting at the level of the Cdc2-cyclin B complex. To confirm this result, the Cdc2-cyclin B complex in ORF20-expressing cells was shown to be essentially without kinase activity. As the ORF20 gene is conserved in all herpesvirus, it may be presumed to have evolved to fulfil an important, as yet undefined, biological role in host-cell modification.  (+info)

Structure of the acidianus filamentous virus 3 and comparative genomics of related archaeal lipothrixviruses. (6/10)

Four novel filamentous viruses with double-stranded DNA genomes, namely, Acidianus filamentous virus 3 (AFV3), AFV6, AFV7, and AFV8, have been characterized from the hyperthermophilic archaeal genus Acidianus, and they are assigned to the Betalipothrixvirus genus of the family Lipothrixviridae. The structures of the approximately 2-mum-long virions are similar, and one of them, AFV3, was studied in detail. It consists of a cylindrical envelope containing globular subunits arranged in a helical formation that is unique for any known double-stranded DNA virus. The envelope is 3.1 nm thick and encases an inner core with two parallel rows of protein subunits arranged like a zipper. Each end of the virion is tapered and carries three short filaments. Two major structural proteins were identified as being common to all betalipothrixviruses. The viral genomes were sequenced and analyzed, and they reveal a high level of conservation in both gene content and gene order over large regions, with this similarity extending partly to the earlier described betalipothrixvirus Sulfolobus islandicus filamentous virus. A few predicted gene products of each virus, in addition to the structural proteins, could be assigned specific functions, including a putative helicase involved in Holliday junction branch migration, a nuclease, a protein phosphatase, transcriptional regulators, and glycosyltransferases. The AFV7 genome appears to have undergone intergenomic recombination with a large section of an AFV2-like viral genome, apparently resulting in phenotypic changes, as revealed by the presence of AFV2-like termini in the AFV7 virions. Shared features of the genomes include (i) large inverted terminal repeats exhibiting conserved, regularly spaced direct repeats; (ii) a highly conserved operon encoding the two major structural proteins; (iii) multiple overlapping open reading frames, which may be indicative of gene recoding; (iv) putative 12-bp genetic elements; and (v) partial gene sequences corresponding closely to spacer sequences of chromosomal repeat clusters.  (+info)

Crystal structure of AFV1-102, a protein from the acidianus filamentous virus 1. (7/10)

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Acidianus filamentous virus 1 coat proteins display a helical fold spanning the filamentous archaeal viruses lineage. (8/10)

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