English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Double-stranded (ds) DNA viruses of the family Lavidaviridae, commonly known as virophages, are a fascinating group of eukaryotic viruses that depend on a coinfecting giant dsDNA virus of the Mimiviridae for their propagation. Instead of replicating in the nucleus, virophages multiply in the cytoplasmic virion factory of a coinfecting giant virus inside a phototrophic or heterotrophic protistal host cell. Virophages are parasites of giant viruses and can inhibit their replication, which may lead to increased survival rates of the infected host cell population. The genomes of virophages are 17–33 kilobase pairs (kbp) long and encode 16–34 proteins. Genetic signatures of virophages can be found in metagenomic datasets from various saltwater and freshwater environments around the planet. Most virophages share a set of conserved genes that code for a major and a minor capsid protein, a cysteine protease, a genome-packaging ATPase, and a superfamily 3 helicase, although the genomes are otherwise diverse and variable. Lavidaviruses share genes with other mobile genetic elements, suggesting that horizontal gene transfer and recombination have been major forces in shaping these viral genomes. Integrases are occasionally found in virophage genomes and enable these DNA viruses to persist as provirophages in the chromosomes of their viral and cellular hosts. As we watch the genetic diversity of this new viral family unfold through metagenomics, additional isolates are still lacking and critical questions regarding their infection cycle, host range, and ecology remain to be answered. Introduction Virophages are a recently discovered class of double-stranded (ds) DNA viruses that have evolved a dependency on complex dsDNA viruses of eukaryotes, so-called giant viruses. The discovery of giant viruses was therefore a prerequisite for the isolation and characterization of virophages (see Fig. 12.1), as shall be reviewed here briefly (See also Reteno et al., 2018). In 1992, following a pneumonia outbreak in Bradford, England, an intra-amoebal parasite was isolated by the team of T.J. Rowbotham and given the name ‘Bradford coccus’. This microorganism was initially assumed to be a bacterium because of its size and positive Gram-stain reaction; however, attempts to amplify and analyse its 16S ribosomal DNA sequences failed. A decade later in the laboratory of Didier Raoult in Marseille, electron microscopy revealed that Bradford coccus was in fact a giant virus with a fibre-studded, 0.75 μm-diameter particle (La Scola et al., 2003). The serendipitous discovery of Acanthamoeba polyphaga mimivirus (family Mimiviridae, genus Mimivirus, species Acanthamoeba polyphaga mimivirus) and the analysis of its 1.2 million base pair dsDNA genome have profoundly changed our view of the viral world (Raoult et al., 2004). This virus exhibited a particle size and genome length that exceeded those of the smallest cellular organisms, blurring the boundary between viruses and cells. The finding that some mimivirus genes were homologous to genes that were previously known to occur only in cellular genomes, in particular four aminoacyl-tRNA synthetases and four translation factors, spurred evolutionary scenarios in which giant viruses were hypothesized to caister.com/cimb 1 Curr. Issues Mol. Biol. Vol. 40

The Virophage Family Lavidaviridae