''Ortervirales'' is an order that contains all accepted species of single-stranded
RNA
Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
viruses that replicate through a
DNA intermediate (Group VI) and all accepted species of double-stranded DNA viruses (except ''
Hepadnaviridae
''Hepadnaviridae'' is a family of viruses. Humans, apes, and birds serve as natural hosts. There are currently 18 species in this family, divided among 5 genera. Its best-known member is hepatitis B virus. Diseases associated with this family i ...
'') that replicate through an RNA intermediate (Group VII).
The name is derived from the reverse of retro.
All reverse-transcribing viruses possess significant similarities to each other. Their
reverse transcriptase
A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genomes, ...
proteins share a common origin. Moreover, belpaoviruses, metaviruses, pseudoviruses, and retroviruses have other features in common. Their
polymerase
A polymerase is an enzyme ( EC 2.7.7.6/7/19/48/49) that synthesizes long chains of polymers or nucleic acids. DNA polymerase and RNA polymerase are used to assemble DNA and RNA molecules, respectively, by copying a DNA template strand using base- ...
proteins are similar in structure and include
aspartic protease
Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the active ...
(
retroviral aspartyl protease
Retroviral aspartyl proteases or retropepsins are single domain aspartyl proteases from retroviruses, retrotransposons, and badnaviruses (plant dsDNA viruses). These proteases are generally part of a larger pol or gag polyprotein. Retroviral ...
) and an
integrase
Retroviral integrase (IN) is an enzyme produced by a retrovirus (such as HIV) that integrates—forms covalent links between—its genetic information into that of the host cell it infects. Retroviral INs are not to be confused with phage int ...
belonging to the DDE recombinase superfamily (see
Recombination-activating gene ">tructure. They also share similar
capsid
A capsid is the protein shell of a virus, enclosing its genetic material. It consists of several oligomeric (repeating) structural subunits made of protein called protomers. The observable 3-dimensional morphological subunits, which may or may ...
and nucleocapsid proteins/domains.
Caulimoviruses also share some features with belpaoviruses, metaviruses, pseudoviruses, and retroviruses such as a homologous
aspartate protease
Aspartic proteases are a catalytic type of protease enzymes that use an activated water molecule bound to one or more aspartate residues for catalysis of their peptide substrates. In general, they have two highly conserved aspartates in the acti ...
. On the other hand, ''Hepadnaviridae'' family appears to be more distantly related to the above-mentioned families.
[
]
Taxonomy
There are five families in this order:
*Family ''Belpaoviridae
''Semotivirus'' is the only genus of viruses in the family ''Belpaoviridae'' (formerly included in the family ''Metaviridae''). Species exist as retrotransposons in a eukaryotic host's genome. BEL/pao transposons are only found in animals.
Spec ...
'' – LTR retrotransposon
LTR retrotransposons are class I transposable element characterized by the presence of long terminal repeats (LTRs) directly flanking an internal coding region. As retrotransposons, they mobilize through reverse transcription of their mRNA and in ...
, Bel/Pao family
*Family ''Metaviridae
''Metaviridae'' is a family of viruses which exist as Ty3-gypsy LTR retrotransposons in a eukaryotic host's genome. They are closely related to retroviruses: members of the family ''Metaviridae'' share many genomic elements with retroviruses, in ...
'' – LTR retrotransposon
LTR retrotransposons are class I transposable element characterized by the presence of long terminal repeats (LTRs) directly flanking an internal coding region. As retrotransposons, they mobilize through reverse transcription of their mRNA and in ...
, Ty3/gypsy family
*Family ''Pseudoviridae
''Pseudoviridae'' is a family of viruses, which includes three genera.
Viruses of the family are actually LTR retrotransposons of the Ty1-copia family. They replicate via structures called virus-like particles (VLPs). VLPs are not infectious l ...
'' – LTR retrotransposon
LTR retrotransposons are class I transposable element characterized by the presence of long terminal repeats (LTRs) directly flanking an internal coding region. As retrotransposons, they mobilize through reverse transcription of their mRNA and in ...
, Ty1/copia family
*Family ''Retroviridae
A retrovirus is a type of virus that inserts a DNA copy of its RNA genome into the DNA of a host cell that it invades, thus changing the genome of that cell. Once inside the host cell's cytoplasm, the virus uses its own reverse transcriptase e ...
'' – Retroviruses, e.g. HIV
The human immunodeficiency viruses (HIV) are two species of ''Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immune ...
*Family ''Caulimoviridae
''Caulimoviridae'' is a family of viruses infecting plants. There are 94 species in this family, assigned to 11 genera. Viruses belonging to the family ''Caulimoviridae'' are termed double-stranded DNA (dsDNA) reverse-transcribing viruses (or pa ...
'' – dsDNA-RT viruses infecting plants
References
{{Taxonbar, from=Q51526792
Virus orders