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RNA virus

(Redirected from Negative-sense ssRNA virus)

An RNA virus is a virus which belongs to either Group III, Group IV or Group V of the Baltimore classification system of classifying viruses. As such, they possess ribonucleic acid (RNA) as their genetic material and do not replicate using a DNA intermediate. The nucleic acid is usually single-stranded RNA (ssRNA) but can occasionally be double-stranded RNA (dsRNA). Notable human pathogenic RNA viruses include SARS, Influenza and Hepatitis C viruses. Walter Fiers (University of Ghent, Belgium) was the first to establish the complete nucleotide sequence of a gene (1972) and of the viral genome of a virus: Bacteriophage MS2-RNA (1976)[1]


Contents

Characteristics

RNA Sense

Main article: Sense (molecular biology)

RNA viruses can be further classified according to the sense or polarity of their RNA into negative-sense and positive-sense RNA viruses. Positive-sense viral RNA is identical to viral mRNA and thus can be immediately translated by the host cell. Negative-sense viral RNA is complementary to mRNA and thus must be converted to positive-sense RNA by an RNA polymerase before translation. As such, purified RNA of a positive-sense virus can directly cause infection though it may be less infectious than the whole virus particle. Purified RNA of a negative-sense virus is not infectious by itself as it needs to be transcribed into positive-sense RNA.

Mutation rates

RNA viruses generally have very high mutation rates as they lack DNA polymerases which can find and fix mistakes, and are therefore unable to conduct DNA repair of damaged genetic material. DNA viruses have considerably lower mutation rates due to the proof-reading ability of DNA polymerases within the host cell. Retroviruses integrate a DNA intermediate of their RNA genome into the host genome, and therefore have a higher chance of correcting any mistakes in their genome thanks to the action of proof-reading DNA polymerases belonging to the host cell.

Although RNA usually mutates rapidly, recent work found that the SARS virus and related RNA viruses contain a gene that mutates very slowly.[2] The gene in question has a complex three-dimensional structure which is hypothesized to provide a chemical function necessary for viral propagation, perhaps as a ribozyme. If so, most mutations would render it unfit for that purpose and would not propagate.

Replication

Animal RNA viruses can be placed into about four different groups depending on their mode of replication.

Group III - dsRNA viruses

Group IV - positive-sense ssRNA viruses

Group V - negative-sense ssRNA viruses

See also

References

  1. ^ Fiers W et al., Complete nucleotide-sequence of bacteriophage MS2-RNA - primary and secondary structure of replicase gene, Nature, 260, 500-507, 1976
  2. ^ Robertson MP, Igel H, Baertsch R, Haussler D, Ares M Jr, Scott WG (2005). "The structure of a rigorously conserved RNA element within the SARS virus genome". PLoS Biol 3 (1): e5. PMID 15630477 DOI:10.1371/journal.pbio.0030005.

Categories


Virology | RNA

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