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Virology Division News 1337

A listing of families and genera with some discriminatory features

M. A. Mayo Scottish Crop Research Institute, Invergowrie, U.K.

For , as for other biological entities, classification and nomenclature are necessary prerequisites for meaningful comparative study and discussion. The way viruses are classified and their taxa are named (i.e. taxonomy) is regulated by the International Committee on the Taxonomy of Viruses (ICTV) which publishes up-dates on previous taxonomies at intervals. The latest taxonomy is the 6th Report of ICTV [3] which describes 165 genera, of which 139 are classified among 50 families. The differences between this and the previous taxonomy [1] were agreed at the plenary meeting of ICTV in 1993 and have been described briefly by Pringle [4] and Mayo and Martelli [2]. The classification scheme is necessarily complex as it deals with viruses which range between the large, complicated poxviruses with virions c. 250 nm x 350 nm which contain up to 400 kbp of ds DNA and simple viruses such as leviviruses and with 25 to 30 nm diameter virions which contain c. 4 kb of ssRNA. However, a Key to the Placement of Viruses in Taxa is given in Murphy et al. [3] which, by using relatively few criteria, distinguishes every from every other genus. A further simplification, based on the Key and designed to illustrate virus diversity in as succinct a manner as possible, is shown in Table 1 (see pp. 1338-1340). Viruses have been divided into 6 categories depending on the nature of their (dsDNA, ssDNA etc.). Below this level a few criteria distinguish genera either grouped into families or individually when no family exists. The criteria are nested from the top left of each category. A version of this Table will be placed on the Internet when ICTV have organized a home page. In the interim, copies can be obtained from the author. Table 1

The da DNA Viruses

Host a prokaryote Host a bacterium; virion with a contractile tall : "T4-1ike phages', Host a bacterium; virion with a > 60 nm long non-contractile tail : "L-like phages" Host a bacterium; virlon with a < 30 nm long non-contractile tail Podoviridae : "T7-1ike phages" Host a bacterium; virion without tails or envelopes DNA linear > 10 kbp Tectiviridae : DNA circular < 10 kbp Corticoviridae : Cotticovirus Host a mycoplasma; virion enveloped Piasmaviridae : Plasmavirus Host an archaebacterium; virion rod-shaped : Lipothrixvirus Host an archaebactedum; virion lemon-shaped : Fusellovirus Host a Virion contains multiple DNA molecules Polydnat4ridae : Virion contains a single large (> 9Okbp) DNA molecule DNA > 300 kbp; virion not enveloped; host an alga : Phycodnavirus DNA usually < 300 kbp; virion enveloped; host an animal Genome covalently closed circular DNA : Nucteopolyhedrovirus Granutovirus Genome linear DNA; nucleocapsid not rod-shaped; Virlen ovoid or brick-shaped : : A vfpoxvirus poxvfrus Iluscipo xvirus L eporipoxvirus Entomopoxwrinae: Entomopoxvirus A Entomopoxvfrus B Entomopoxvirus C Genome linear DNA; virion not ovoid or brick-shaped Virion ~cosahedral with 70 - 100 nm diameter cores; virus multiplies in ticks and swine "African swine fever-like viruses" Virion icosahedral; genome circularly permutated and terminally redundant; host a pctkitothermic tridoviridae : lridovirus Lymphocystivirus "Goldfish virus 1-like viruses" Virion quasi-spherical with 100 - 110 nm diameter cores; genome not circularly permutated; host a vertebrate : A/phaherpesvirinae: : Cytomegalowus Gammaherpesvirfnae : Lyrnphocryptov~rus Rhadinotdrus Viruses with a single molecule of small (<90kbp) DNA DNA < 30 kbp Papovaviridae : Polyomavirus PapillomavJrus DNA > 30 kbp Host a Rhi~virus Host a vertebrate : A viadenov~rus

The =mONA Viruses

Host a prokaryote Virion has helical symmetry fnoviridae : ~nov#us Plectrovfrus Virion icosahedral : f~crovims Bdeflomicrot4rus Host a : "subgroup I Geminivirus" "subgroup 11Geminivirus" "subgroup III Geminivirus" Host an animal DNA circular : DNA linear P arvo viridae : Parvowrinae : Dependovirus Parvovirus Erythrovirus Densovirinae: Denso virus tteravirus Table 1 (continued) Contravirus Division News 1339

The DNA and RNA reverse Transcribing Viruses

Virions contain DNA; host a vertebrate : OrthohepadnavJrus A Vihepadnavirus Virions contain DNA; host a plant Virion bacilliform Badnawrus Yirion icosahedral Virions contain RNA Retroviridae: LentMres "mammalian type B " Spumavirus "avian type C retroviruses" "mammalian type D retroviruses" "mammalian type C retroviruses" "MHTLV-ELV retroviruses"

The dsRNA Viruses

Host a prokaryote CystovJridae : Host a eukaryote Genome in > 9 segments Beoviridae : OrthoreovJrus OrbMrus Botav#us FijMrus Genome in < 9 segment Host an animal BtrnavMdae : Entomobirnavtrus Aquabimavirus A vibimavirus Host not an animal No virions are formed in diseased tissue Hypowridae : HypovJrus RNA is encapsidated Genome monopartite : L eish mania virus Genome multipartite -- PartitMridae : Parlitivirus Chrysovirus Alphacryptot,#us Befacryptovirus

The Negative Sense ssRNA Viruses

RNA circular; productive multiplication is -dependent Deltavirus RNA linear Genome monopartite (order ) Virion filamentous and/or pleomorphic; RNA t 8-19 kb -- Filovfridae : Filovirus Virion pleomorphic, usually spherical; RNA 15-t 6kb : Pneumovirinae: Pneumovirus Paramyxovirinae: Paramyxovirus RubulavJrus Virion bullet-shaped or bacilliform; RNA 11 to 15 kb : L yssawrus Vesiculovirus Ephemerov~res NucleorhabdovJrus Genome multipartife Genome in > 5 segments : Influenza virus A, B Influenza virus C =Thogoto-like viruses" Genome bipartite; Virion contains host ribosomes Arenaviridae : Genome tripartite; virion does not contain host ribosomes -- BunyavMdae : Bunyav#us NairovJrus Hantavfrus Phlebovirus Tospovirus Genome in < 5 segments TenuMrus

Table 1 (continued) 1340 Virology Division News

The Positive Sense ssRNA viruses

Host a prokaryote Levividdae : Levivirus AIIolevivirus Host a eukaryote No virlons formed except in the coat of a heterologeus virus Umbravirus Vidons enveloped Genome expressed as a polyprotein, no sub-genomic formed -- Flavividdae : Fla viviru s Pestivirus "Hepatitis C-like viruses" Sub-genomic RNA are formed in infected cells Infected cells contain 1 species of sub-genomic RNA Togaviridae : Rubivirus Infected cells contain >1 species of subgenomic RNA; genome > 20 kb : Ooronavirus Infected cells contain >1 species of subgenomic RNA; genome < 20 kb Artedvirus

Virlon not enveloped Coat protein(s) are expressed by proteotysis of a large (Mr > 100 x 103 ) polyprotein Host an animal; N-terminus of structural at or within c.300 residues of the N-terminus of the polyprotein ---- Picomaviridae : Cardlovfrus Hepatovirus Host a plant; structural proteins preceded upstream in the polyprotele by >400 residues of non-structural protein Virion filamentous : ymovirus Virlon isometric; genome monopartife Sequiviridae : equivirus Virion isometric; genome bipartite Comoviddae : Fabav~rus Coat protein{s) expressed by translation of a small genome segment or a subgenomic RNA Host a vertebrate; vidon has cup-shaped depressions and contains one structural protein : C alicivirus Host a vertebrate; virion often star-shaped and contains 2 or 3 structural proteins Astroviridae : Host an invertebrate; structural protein Mr < 40 x 103 Nodat4ridae : Nodavirus Host an invertebrate; structural protein Mr > 60 x t03 Tetraviridae : "Nudaurelia capensis 8 -like viruses" "Nudaurelia capensis ~o -like viruses= Host a plant or a fungus Virus circulates in the bodies of the vectors Vector a Vector an ; virus not transmissible mechanically Vector an aphid; virus readily transmissible mechanically No vector known or transmission non-circulative Virion isometric or bacilliform Host a fungus; virlon bacilliform Bamaviridae : Barnavirus Host not a fungus Genome monopartite; RNA about 6 kb TymovJrus Genome monopartite; RNA < 4 kb; vector a fungus Necrovirus Genome monopartite; RNA > 4 kb; vector an Coat protein Mr > 35 x 103 : Carmovims Coat protein Mr c. 30 x 103 ; RNA has VPg Sobemovirus Coat protein c. 25 x 10s; RNA has cap Genome bipartite; larger genome RNA < 4 kb Dianthovirus Genome bipartite; larger genome RNA > 5 kb Maeot4rus Genome tdparlite : Bromot#rus Affamovirus tlarvirus Virion rod-shaped; genome monopartite Genome multipartite; virion > 20 nm in diameter; vector a ...... Virlon < 20 nm in diameter; largest RNA > 5 kb; vector a fungus ...... Virion < 20 nm in diameter; largest RNA < 5 kb Hordeiv#us Virlon filamentous Virion > 700 nm in length Virion < 600 nm in length; coat protein Mr < 25 x 103 Potexvirus Virion > 600 nm; coat protein Mr > 25 x 103 Virlon with prominent banding; genome lacks a triple gene block Replicase and coat protein encoded in the same open reading frame Non-structural and coat proteins encoded in different open reading frames Virlon without obvious banding; genome contains a triple gene block --

Table I (cot~tinued) Virology Division News 1341

References 1. Francki RIB, Fauquet CM, Knudson DL, Brown F (1991) Classification and Nomenclature of Viruses. Fifth Report of the International Committee on Taxonomy of Viruses. Springer, Wien New York (Arch Virol [Suppl] 2) 2. Mayo MA, Martelli GP (1993) New families and genera of plant viruses. Arch Virol 133:496-498 3. Murphy FA, Fauquet CM, Bishop DHL, Ghabrial SA, Jarvis AW, Martelli GP, Mayo MA, Summers MD (1995) Virus Taxonomy. Classification and Nomenclature of Viruses. Sixth Report of the International Committee on Taxonomy of Viruses. Springer, Wien New York (Arch Virol [Suppl] 10) 4. Pringle CR (1993) Virus taxonomy update. Arch Virol 133:491-495

Author's address: Dr. M. A. Mayo, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, U.K.