Table 1701

Families of Viruses

Virus Family Typical Examples

Double-Stranded DNA Viruses

Myoviridae T4-like bacteriophages

Siphoviridae lambda-like bacteriophages

Fuselloviridae bacteriophages of Sulfolobus

Poxviridae cowpox, Vaccinia, smallpox (= Variola), ectromelia

Baculoviridae baculoviruses of insects

Herpesviridae herpes, chickenpox (Varicellavirus)

Adenoviridae adenovirus

Single-Stranded DNA Viruses

Inoviridae small filamentous bacteriophage e.g. fd

Microviridae small spherical bacteriophage e.g. FX174

Geminiviridae assorted plant viruses, e.g. beet curly top virus

Parvoviridae parvoviruses, adeno-associated virus

Reverse Transcribing Viruses

Hepadnaviridae hepatitis B virus, cauliflower mosaic virus

Retroviridae human immunodeficiency virus (HIV)

Double-Stranded RNA Viruses

Reoviridae reoviruses, bluetongue virus of sheep, rotaviruses

Birnaviridae Drosophila X virus

Totiviridae Saccharomyces cerevisiae virus L-A

Negative Single-Stranded RNA Viruses

Paramyxoviridae parainfluenza, measles, mumps

Rhabdoviridae vesicular stomatitis virus, rabies

Filoviridae Marburg virus, Ebola virus

Orthomyxoviridae influenza

Bunyaviridae hantavirus, tomato spotted wilt virus

Positive Single-Stranded RNA Viruses

Leviviridae bacteriophages MS2 and Qp

Picornaviridae polio, common cold (Rhinovirus), hepatitis A, foot-and-mouth virus

Tombusviridae tobacco necrosis virus (TNV)

Flaviviridae yellow fever, hepatitis C

Togaviridae rubella (German measles), tobacco mosaic virus (TMV)

Virus particles come in a wide range of sizes and shapes.

must provide a special RNA polymerase to replicate their RNA genomes, an RNA replicase.

Viruses may also be classified according to the structure of the virus particle, or virion. The three major shapes seen are spherical, filamentous and complex. Spherical viruses are not truly spherical but have 20 triangular faces and are thus icosahedrons (Fig. 17.10). Cross sections through an icosahedron may be five- or six-sided depending on where the cut is made. As with most other biological filaments, filamentous viruses consist of helically arranged protein subunits forming cylindrical shells. These may be either open or closed off at the ends. Complex viruses are large viruses with multiple structural components that do not fit neatly into the spherical versus filamentous classification. In addition, outer envelopes, partly derived from the cytoplas-mic membrane of the previous host cell, surround some virus particles (Fig. 17.11).

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