Zamilon virophage

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Mimivirus-dependent virus Zamilon
Two Zamilon virophages (inset) to scale with their associated giant virus Megavirus [1]
Virus classification Edit this classification
(unranked): Virus
Realm: Varidnaviria
Kingdom: Bamfordvirae
Phylum: Preplasmiviricota
Class: Maveriviricetes
Order: Priklausovirales
Family: Lavidaviridae
Genus: Sputnikvirus
Species:
Mimivirus-dependent virus Zamilon

Mimivirus-dependent virus Zamilon, or Zamilon, is a

polypeptides
. A related strain, Zamilon 2, has been identified in North America.

All known virophages are associated with helpers in the

CRISPR-Cas pathway.[4]
Unlike the Sputnik virophage, Zamilon does not appear to impair the replication of its helper virus.

Discovery and related virophages

Zamilon was discovered in 2013, in

Mavirus; several other virophage DNAs have been discovered using metagenomics but have not been characterised physically.[2][6] A related strain, named Zamilon 2, was discovered by metagenomic analysis of a North American poplar wood chip bioreactor in 2015.[7] Another virophage, Rio Negro, is also closely related to Sputnik.[2]

Taxonomy

Zamilon virophage has been classified by the

Lavidaviridae.[2]

Virology

A Zamilon virion is spherical with a diameter of 50–60 nm, and is similar in appearance to those of Sputnik and Mavirus.[3] Its circular double-stranded DNA genome is 17,276 base pairs in length.[2][3] Virophages typically have particles whose diameter is in the range 40–80 nm, with genomes in the range 17–30 kb.[2] The virophage most closely related to Zamilon is Sputnik, with which it shares 76% sequence identity, although part of the Zamilon sequence is reversed compared with Sputnik.[2][3] Zamilon's DNA is rich in adenine and thymine bases; the proportion of guanine and cytosine bases is 29.7%.[3]

Open reading frames

The Zamilon genome is predicted to contain 20

Mavirus, and another to Organic Lake virophage and a Phaeocystis globosa virophage, which are both associated with algae rather than amoebae. The remaining two predicted products show limited similarity to other known proteins. Putative functions of the products include transposase, helicase, integrase, cysteine protease, DNA primase–polymerase and DNA-packaging ATPase enzymes, major and minor capsid proteins, a structural protein and a collagen-like protein.[3] ORF6 is very similar to the Sputnik major capsid protein, which has a double "jelly-roll" fold.[3][8]

ORF[a] Predicted size
(amino acids) 		Related product Similarity
(%) 		Predicted function
1 111 none – –
2 73 none – –
3 135 Megavirus chilensis mg3 gene product 67 –
4 221 Sputnik virophage 2 putative IS3 family transposase A protein 40 putative transposase
5 376 Sputnik virophage 2 minor virion protein 66 minor virion protein
6 609 Sputnik virophage capsid protein V20 86 capsid protein
7 442 Sputnik virophage V21 70 –
8 81 Moumouvirus monve hypothetical protein tv_L8 72 –
9 778 Sputnik virophage V13 67 putative helicase
10 168 Sputnik virophage V11 53 –
11 247 Sputnik virophage V10 58 putative integrase
12 175 Sputnik virophage V9 77 –
13 184 Sputnik virophage V8 71 structural protein
14 241 Sputnik virophage V7 80 –
15 305 Sputnik virophage V6 75 collagen-like protein
16 121 Sputnik virophage V5 59 –
17 133 Sputnik virophage V4 55 –
18 245 Sputnik virophage V3 81 DNA-packaging ATPase
19 147 Megavirus chilensis mg664 gene product 50 –
20 147 Sputnik virophage V1 60 –

Life cycle and helper virus

Like all other virophages, Zamilon replicates in the

virus factory of its helper, which acts as its host.[3] Zamilon was first isolated in association with Mont1, a Mimivirus-like Mimiviridae classified in lineage C by its polymerase B gene sequence. The virophage has subsequently been shown to be capable of replicating in association with Moumouvirus and Monve, two Mimiviridae from lineage B, as well as with Terra1 and Courdo11 from lineage C; however, it cannot replicate in association with either Mimivirus or Mamavirus, classified as lineage A.[3][9] This is unlike Sputnik, which can replicate in association with any Mimivirus-like member of Mimiviridae.[3]

Zamilon does not appear to inhibit the ability of its helper virus to replicate significantly, nor to

virions in the presence of Zamilon, these were also observed at a comparable level in the virophage's absence.[3] This is again unlike Sputnik, which reduces its helper virus's infectivity, inhibits its lysis of amoeba, and is associated with the generation of an increased proportion of abnormal Mimiviridae virions.[2][3] Bernard La Scola and colleagues, who isolated both Sputnik and Zamilon, state that, if confirmed, this "would question the concept of virophage", which has been considered to be differentiated from most other satellite viruses in having a deleterious effect on its helper virus.[3]

References

  1. ^ All data from Gaia et al.[3]
  1. doi:10.1371/journal.ppat.1007592. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License
    .
  2. ^
    PMID 26446887
  3. ^
    PMID 24747414
  4. S2CID 4382855
  5. PMID 23298151
  6. PMID 25909276
  7. PMID 26640459
  8. PMID 23091035
  9. PMID 25104553

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Zamilon_virophage&oldid=1193829359"