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Dicistroviridae

The Dicistroviridae are a family of Group IV (positive-sense ssRNA) insect-infecting viruses. Some of the insects commonly infected by dicistroviruses include aphids, leafhoppers, flies, bees, ants, silkworms.

Taxonomy[edit]

Although many dicistroviruses were initially placed in the Picornaviridae they have since been reclassified into their own family. The name (Dicistro) is derived from the characteristic dicistronic arrangement of the genome.

This family is a member of the 'picornavirus-like superfamily' (Comoviridae, Iflavirus, Picornaviridae, Potyviridae and Sequiviridae). Within this superfamily the gene order is the gene order of the non-structural proteins Hel(helicase)-Pro(protease)-RdRp(polymerase). The Dicistroviridae can be distinguished from the members of the taxa by the location of their structural protein genes at the 3' end rather than the 5' end (as found in Iflavirus, Picornaviridae and Sequiviridae) and by having 2 genomic segments rather than a single one (as in the Comoviridae).

This family has been divided into two genera and a number of as yet unclassified species.

Other species:

RNA structural elements[edit]

Many of the Dicistroviridae genomes contains structured RNA elements. For example, the Cripaviruses have an internal ribosome entry site,[1] which mimics a Met-tRNA and is used in the initiation of translation.[2]

References[edit]

  1. ^ Kanamori, Y; Nakashima N (2001). "A tertiary structure model of the internal ribosome entry site (IRES) for methionine-independent initiation of translation". RNA 7 (2): 266–274. doi:10.1017/S1355838201001741. PMC 1370084. PMID 11233983. 
  2. ^ Malys N, McCarthy JEG (2010). "Translation initiation: variations in the mechanism can be anticipated". Cellular and Molecular Life Sciences 68 (6): 991–1003. doi:10.1007/s00018-010-0588-z. PMID 21076851. 
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Cripavirus

Cripaviruses are a genus of + sense, single-stranded RNA (ssRNA) viruses. It can produce proteins directly from their RNA genome upon entering a cell; and therefore, does not require an RNA polymerase packaged in with it, as this may be produced from the genome after entering the cell.[1]

The genome is 8500–9500 nucleotides long, and has a VPg (genome linked viral protein) on the 5' end. The 5' end also has a series of C's near it, while the 3' end has a series of A's near it.

These viruses have capsids of 12 capsomers but no envelope, and are round 27–30 nm in diameter with an icosahedral symmetry.

The name of the cripavirus family originates from its most famous member the Cricket Paralysis Virus.[1] Which was made famous by its rather unique IRES (Internal Ribosome Entry Site): the Cripavirus IRES. The Cripavirus IRES is an RNA element that allows the virus to bind the ribosome and translate without a need for any initiation factors[2] – as initiation is the most regulated step of translation this allows the virus to avoid many mechanisms to inhibit viral activity.

References [edit]

  1. ^ a b International Committee on the Taxonomy of Viruses
  2. ^ "Structure and Function of Regulatory RNA Elements", Biochimica et Biophysica Acta 1789, 2009: 542–557, PMID 19632368 
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