Virophages go nuclear in the marine alga
            <i>Bigelowiella natans</i>

Fischer, Matthias

doi:10.1073/pnas.1515142112

Cited by 11 publications

(18 citation statements)

References 18 publications

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“…In an extensive genomic analysis for virophage signatures in eukaryotic genomes [39,122], Blanc et al screened more than 1000 genomes including those from protists, fungi, and basal metazoans. Four virophage core proteins families were used as signature genes, including a DNA-packaging ATPase, a cysteine protease, a MCP, and a mCP.…”

Section: Virophages As Mobile Genetic Elements Of Giant Viruses Anmentioning

confidence: 99%

Virophages of Giant Viruses: An Update at Eleven

Mougari

Sahmi-Bounsiar

Levasseur

et al. 2019

Viruses

113

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The last decade has been marked by two eminent discoveries that have changed our perception of the virology field: The discovery of giant viruses and a distinct new class of viral agents that parasitize their viral factories, the virophages. Coculture and metagenomics have actively contributed to the expansion of the virophage family by isolating dozens of new members. This increase in the body of data on virophage not only revealed the diversity of the virophage group, but also the relevant ecological impact of these small viruses and their potential role in the dynamics of the microbial network. In addition, the isolation of virophages has led us to discover previously unknown features displayed by their host viruses and cells. In this review, we present an update of all the knowledge on the isolation, biology, genomics, and morphological features of the virophages, a decade after the discovery of their first member, the Sputnik virophage. We discuss their parasitic lifestyle as bona fide viruses of the giant virus factories, genetic parasites of their genomes, and then their role as a key component or target for some host defense mechanisms during the tripartite virophage–giant virus–host cell interaction. We also present the latest advances regarding their origin, classification, and definition that have been widely discussed.

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Section: Virophages As Mobile Genetic Elements Of Giant Viruses Anmentioning

confidence: 99%

Virophages of Giant Viruses: An Update at Eleven

Mougari

Sahmi-Bounsiar

Levasseur

et al. 2019

Viruses

113

View full text Add to dashboard Cite

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“…The first observation of virophage integration came from the analysis of a mimivirus genome, in which an integrated copy of the Sputnik 2 virophage genome (provirophage) has been identified [29]. This remained an isolated finding until a large scale survey of eukaryotic genome assemblies has revealed multiple remnants of integrated virophages of the Sputnik group as well as giant viruses in the genome of the alga (Chlorarachniophyte) Bigelowiella natans [31,32] The majority of the virophage-derived sequences in the B. natans genome were fragments of deteriorated virophage genomes but 6 potentially active copies with TIRs have been identified [31]. Conserved virophage inserts have been detected in multiple strains of B. natans showing that the virophages can persist in the host genome for substantial time intervals.…”

Section: Integrating Virophages Function As An Adaptive Immune Systemmentioning

confidence: 99%

Polintons, virophages and transpovirons: a tangled web linking viruses, transposons and immunity

Koonin

Krupovìč

2017

Current Opinion in Virology

109

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Virophages are satellite DNA viruses that depend for their replication on giant viruses of the family Mimiviridae. An evolutionary relationship exists between the virophages and Polintons, large self-synthesizing transposons that are wide spread in the genomes of diverse eukaryotes. Most of the Polintons encode homologs of major and minor icosahedral virus capsid proteins and accordingly are predicted to form virions. Additionally, metagenome analysis has led to the discovery of an expansive family of Polinton-like viruses (PLV) that are more distantly related to bona fide Polintons and virophages. Another group of giant virus parasites includes small, linear, double-stranded DNA elements called transpovirons. Recent in-depth comparative genomic analysis has yielded evidence of the origin of the PLV and the transpovirons from Polintons. Integration of virophage genomes into genomes of both giant viruses and protists has been demonstrated. Furthermore, in an experimental coinfection system that consisted of a protist host, a giant virus and an associated virophage, the virophage integrated into the host genome and, after activation of its expression by a superinfecting giant virus, served as an agent of adaptive immunity. There is a striking analogy between this mechanism and the CRISPR-Cas system of prokaryotic adaptive immunity. Taken together, these findings show that Polintons, PLV, virophages and transpovirons form a dynamic network of integrating mobile genetic elements that contribute to the cellular antivirus defense and host-virus coevolution.

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“…The virophages outside the Mavirus group lack the RVE but recently many of them have been shown to encode a distinct subfamily of tyrosine recombinases that is likely to function as an integrase [13]. Indeed, integration of virophages into the genomes of giant viruses [32] and even more notably, into the genome of a cellular organism, the green alga Bigelowiella natans [33,34], has been demonstrated. Most virophages also lack the DNAP gene but recently, a new group of putative virophages has been assembled from the sheep rumen metagenome and shown to encode a DNAP related to the polinton-encoded polymerases [26].…”

Section: Polintons Virophages Polinton-like Viruses: a Distinct Clamentioning

confidence: 99%

Self-synthesizing transposons: unexpected key players in the evolution of viruses and defense systems

Krupovìč

Koonin

2016

Current Opinion in Microbiology

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Self-synthesizing transposons are the largest known transposable elements that encode their own DNA polymerases (DNAP). The Polinton/Maverick family of self-synthesizing transposons is widespread in eukaryotes and abundant in the genomes of some protists. In addition to the DNAP and a retrovirus-like integrase, most of the polintons encode homologs of the major and minor jelly-roll capsid proteins, DNA-packaging ATPase and capsid maturation protease. Therefore, polintons are predicted to alternate between the transposon and viral lifestyles although virion formation remains to be demonstrated. Polintons are related to a group of eukaryotic viruses known as virophages that parasitize on giant viruses of the family Mimiviridae and another recently identified putative family of polinton-like viruses (PLV) predicted to lead a similar, dual life style. Comparative genomic analysis of polintons, virophages, PLV and the other viruses with double-stranded (ds)DNA genomes infecting eukaryotes and prokaryotes suggests that the polintons evolved from bacterial tectiviruses and could have been the ancestors of a broad range of eukaryotic viruses including adenoviruses and members of the proposed order “Megavirales” as well as linear cytoplasmic plasmids. Recently, a group of predicted self-synthesizing transposons was discovered also in prokaryotes. These elements, denoted casposons, encode a DNAP and a homolog of the CRISPR-associated Cas1 endonuclease that has an integrase activity but no capsid proteins. Thus, unlike polintons, casposons appear to be limited to the transposon life style although they could have evolved from viruses. The casposons are thought to have played a pivotal role in the origin of the prokaryotic adaptive immunity, giving rise to the adaptation module of the CRISPR-Cas systems.

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Virophages go nuclear in the marine alga Bigelowiella natans

Cited by 11 publications

References 18 publications

Virophages of Giant Viruses: An Update at Eleven

Virophages of Giant Viruses: An Update at Eleven

Polintons, virophages and transpovirons: a tangled web linking viruses, transposons and immunity

Self-synthesizing transposons: unexpected key players in the evolution of viruses and defense systems

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