Zamilon virophage

Zamilon virophage
Electron micrograph of a virus factory in an amoeba co-infected with Zamilon (small particles) and Mont1. Arrows show abnormal Mont1 particles (scale bar: 0.1 μm)
Virus classification
Group:	Group I (dsDNA)
Order:	Unassigned
Family:	Lavidaviridae
Genus:	Sputnikvirus
Species:	Mimivirus-dependent virus Zamilon

Zamilon is a virophage, a group of small DNA viruses that infect protists and require a helper virus to replicate; they are a type of satellite virus. Discovered in 2013 in Tunisia, infecting Acanthamoeba polyphaga amoebae, Zamilon most closely resembles Sputnik, the first virophage to be discovered. The name is Arabic for "the neighbour". Its spherical particle is 50–60 nm in diameter, and contains a circular double-stranded DNA genome of around 17 kb, which is predicted to encode 20 polypeptides. A related strain, Zamilon 2, has been identified in North America.

All known virophages are associated with helpers in the giant DNA virus family Mimiviridae. Zamilon is restricted in its range of helper viruses; it can be supported by viruses from Mimivirus-like Mimiviridae lineages B and C, but not from lineage A. This appears to be a consequence of a rudimentary immune system of the helper virus, termed MIMIVIRE (mimivirus virophage resistance element), akin to the CRISPR-Cas pathway. Unlike the Sputnik virophage, Zamilon does not appear to impair the replication of its helper virus.

Zamilon was discovered in 2013, in Acanthamoeba polyphaga amoebae co-infected with the giant virus Mont1, isolated from a Tunisian soil sample. As of 2015, Zamilon is one of three virophages to have been isolated physically, the others being Sputnik and Mavirus; several other virophage DNAs have been discovered using metagenomics but have not been characterised physically. A related strain, named Zamilon 2, was discovered by metagenomic analysis of a North American poplar wood chip bioreactor in 2015. Another virophage, Rio Negro, is also closely related to Sputnik.

...
Wikipedia