DNA virus

A DNA virus is a virus that has DNA as its genetic material and replicates using a DNA-dependent DNA polymerase. The nucleic acid is usually double-stranded DNA (dsDNA) but may also be single-stranded DNA (ssDNA). DNA viruses belong to either Group I or Group II of the Baltimore classification system for viruses. Single-stranded DNA is usually expanded to double-stranded in infected cells. Although Group VII viruses such as hepatitis B contain a DNA genome, they are not considered DNA viruses according to the Baltimore classification, but rather reverse transcribing viruses because they replicate through an RNA intermediate. Notable diseases like smallpox, herpes, and the chickenpox are caused by such DNA viruses.

Group I: dsDNA viruses

HHV-6 genome
Genome of human herpesvirus-6, a member of the family Herpesviridae

Genome organization within this group varies considerably. Some have circular genomes (Baculoviridae, Papovaviridae and Polydnaviridae) while others have linear genomes (Adenoviridae, Herpesviridae and some phages). Some families have circularly permuted linear genomes (phage T4 and some Iridoviridae). Others have linear genomes with covalently closed ends (Poxviridae and Phycodnaviridae).

A virus infecting archaea was first described in 1974. Several others have been described since: most have head-tail morphologies and linear double-stranded DNA genomes. Other morphologies have also been described: spindle shaped, rod shaped, filamentous, icosahedral and spherical. Additional morphological types may exist.

Orders within this group are defined on the basis of morphology rather than DNA sequence similarity. It is thought that morphology is more conserved in this group than sequence similarity or gene order which is extremely variable. Three orders and 31 families are currently recognised. A fourth order — Megavirales — for the nucleocytoplasmic large DNA viruses has been proposed.[1][2] This proposal has yet to be ratified by the ICTV. Four genera are recognised that have not yet been assigned a family.

Fifteen families are enveloped. These include all three families in the order Herpesvirales and the following families: Ascoviridae, Ampullaviridae, Asfarviridae, Baculoviridae, Fuselloviridae, Globuloviridae, Guttaviridae, Hytrosaviridae, Iridoviridae, Lipothrixviridae, Nimaviridae and Poxviridae.

Bacteriophages (viruses infecting bacteria) belonging to the families Tectiviridae and Corticoviridae have a lipid bilayer membrane inside the icosahedral protein capsid and the membrane surrounds the genome. The crenarchaeal virus Sulfolobus turreted icosahedral virus has a similar structure.

The genomes in this group vary considerably from ~10 kilobases to over 2.5 megabases in length. The largest bacteriophage known is Klebsiella Phage vB_KleM-RaK2 which has a genome of 346 kilobases.[3]

The virophages are a group of viruses that infect other viruses.

A virus with a novel method of genome packing infecting species of the genus Sulfolobus has been described.[4] As this virus does not resemble any known virus it has been classified into a new family, the Portogloboviridae.

Another Sulfolobus infecting virus - Sulfolobus ellipsoid virus 1 - has been described.[5] This enveloped virus has a unique capsid and may be classified into a new taxon.

Host range

Species of the order Caudovirales and of the families Corticoviridae and Tectiviridae infect bacteria.

Species of the order Ligamenvirales and the families Ampullaviridae, Bicaudaviridae, Clavaviridae, Fuselloviridae, Globuloviridae, Guttaviridae and Turriviridae infect hyperthermophilic archaea species of the Crenarchaeota.

Species of the order Herpesvirales and of the families Adenoviridae, Asfarviridae, Iridoviridae, Papillomaviridae, Polyomaviridae and Poxviridae infect vertebrates.

Species of the families Ascovirus, Baculovirus, Hytrosaviridae, Iridoviridae and Polydnaviruses and of the genus Nudivirus infect insects.

Species of the family Mimiviridae and the species Marseillevirus, Megavirus, Mavirus virophage and Sputnik virophage infect protozoa.

Species of the family Nimaviridae infect crustaceans.

Species of the family Phycodnaviridae and the species Organic Lake virophage infect algae. These are the only known dsDNA viruses that infect plants.

Species of the family Plasmaviridae infect species of the class Mollicutes.

Species of the family Pandoraviridae infect amoebae.

Species of the genus Dinodnavirus infect dinoflagellates. These are the only known viruses that infect dinoflagellates.

Species of the genus Rhizidiovirus infect stramenopiles. These are the only known dsDNA viruses that infect stramenopiles.

Species of the genus Salterprovirus and Sphaerolipoviridae infect species of the Euryarchaeota.

Taxonomy

Unclassified viruses

A group of double stranded DNA viruses have been found in fish that appear to be related to the herpesviruses.[6]

Another group of viruses that infect fish has been described.[7]

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