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Family	00.097.   Pseudoviridae
	Taxonomic Structure of the Family
	Family         00.001. Pseudoviridae Genus                      00.097.0.01.   Pseudovirus Genus                      00.097.0.02.   Hemivirus Genus                      00.097.0.03.   Sirevirus

List of Species Demarcation Criteria in the Genus

In general, viruses inhabiting different host species will be considered different species, because they will have diverged through vertical descent from a common ancestor at least as much as the host species themselves (probably more so, due to the error-prone mechanism of replication). However, there are instances in the family Pseudoviridae and the family Metaviridae in which one finds two closely related viruses inhabiting the same host species, e.g. Ty1 and Ty2 of S. cerevisiae and Tf1 and Tf2 of S. pombe. In both of these pairs of viruses, the RT as sequences are quite similar. However, the capsid-encoding sequences are significantly diverged (e.g. < 50% as sequence identity; their DNA sequences fail to cross hybridize). The question then arises whether these represent different species or more subtle variants. We have considered such viruses separate species if at least one of the major coding regions (e.g. capsid) is <50% identical to the reference as sequence. For example, Ty1 and Ty2 Gag as sequences are 49% identical.

Individual species within the genus Sirevirus all have greater than 50% identity in their RT as sequences. Members of the genera Pseudovirus, Hemivirus and the Phaseolus vulgaris Tpv2-6 virus (Tpv2-6) group share less than 45% identity to sirevirus RTs.

List of Species in the Genus

The ICTVdB virus code and the virus names. Species names are in italics. All other virus names are not italicized and their taxonomic status is color-coded as follows: alternative names (synonym), isolates, strains, serotypes, subspecies, reclassified or rejected names.

 
Virus codes, virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

None reported.

List of Species in the Genus

The ICTVdB virus code and the virus names. Species names are in italics. All other virus names are not italicized and their taxonomic status is color-coded as follows: alternative names (synonym), isolates, strains, serotypes, subspecies, reclassified or rejected names.

 
Virus codes, virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

None reported.

List of Species in the Genus

The ICTVdB virus code and the virus names. Species names are in italics. All other virus names are not italicized and their taxonomic status is color-coded as follows: alternative names (synonym), isolates, strains, serotypes, subspecies, reclassified or rejected names.

 
Virus codes, virus names, genome sequence accession numbers [ ], and assigned abbreviations ( ), are:

Species, their serotypes, strains and isolates

Tentative Species in the Genus

None reported.

List of Unassigned Viruses in the Family

Similarity with Other Taxa

Like members of the Families Hepadnaviridae and Metaviridae, the members of the Family Pseudoviridae are clearly related to the members of the Family Retroviridae. All four families are linked by reverse transcription and a viral core structure made up of gag-like proteins. Members of the Family Pseudoviridae are different from the other two in that all lack env-like genes and have the unusual organisation (PR-IN-RT-RH) of pol. Members of the Families Pseudoviridae, Metaviridae, and Retroviridae also share the following: a proviral form characterised by LTRs, protease, RNase H, and integrase activities essential for multiplication, readthrough-mediated gag-pal gene expression, and tRNA primers (in most species).

An important and controversial question is the extent of the relationship between the members of the families Pseudoviridae, Metaviridae, and Retroviridae. Because the genomic structures of elements in the families Pseudoviridae and Metaviridae are clearly related to, but simpler than, those of members of the family Retroviridae, many authors who have considered the problem have concluded that the Families Pseudoviridae and Metaviridae represent more primitive groups; the members of the Family Metaviridae probably spawned the members of the family Retroviridae (presumably by transducing genes encoding ligands for cell surface receptors) This conclusion makes sense within the context of the enormous diversity of other types of retroelements, which are all clearly phylogenetically related by the presence of RT, but not all of which encode a virus-like intermediate. An alternative view-point that cannot be ruled out, but for which there is less support, is that members of the Family Metaviridae represent degenerate forms of members of the Family Retroviridae.

Derivation of Name

Hemi: from Greek hemi, "half", referring to the half-molecule of tRNA used as a primer for reverse transcription.
Pseudo: from Greek pseudo, "false", to connote some uncertainty as to whether these are true viruses.

References

Collated from VIIIth ICTV Report

Contributed by

Boeke JD, Eickbush T, Sandmeyer SB, and Voytas DF

Version 4 is based on Virus Taxonomy, Classification and Nomenclature of Viruses, 8th ICTV Report of the International Committee on Taxonomy of Viruses. Fauquet, CM, Mayo, MA, Maniloff, J, Desselberger, U, and Ball, LA (EDS) (2005) Elsevier/Academic Press, pp. 1259.

Additional References

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