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Viral Stranding and Segmentation

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Topic updated on 03/15/15 6:34pm

Introduction
  • Viral nucleic acids (DNA or RNA) can be classified into
    • positive vs. negative stranded
    • segmented vs. nonsegmented
Positive vs. Negative Stranded
  • Positive-stranded RNA
    • is just like mRNA
    • can be read natively by the host's translational machinery to make proteins
  • Negative-stranded RNA
    • is complementary to mRNA
    • must be transcribed into a positive strand by the virus's own RNA-dependent RNA polymerase
      • this enzyme is carried in the capsid of all negative-stranded RNA viruses
  • Most DNA viruses have both a positive and negative strand
    • except parvoviruses, which are single-stranded
    • however, the meaning of "positive strand" or "negative strand" is not the same as for an RNA virus
      • positive strand is the strand that is read
      • negative strand is the strand that is ignored
  • A list of positive vs. negative stranded RNA viruses can be found in the table of RNA viruses
Segmented vs. Nonsegmented
  • The viral genome is sometimes found split into separate parts, a phenomenon known as segmenting
  • The segmented viruses are all RNA viruses
    • bunyaviruses
      • e.g. hantavirus
    • orthomyxoviruses
      • e.g. influenza
        • contains 8 segments that can undergo reassortment
          • contributes to flu pandemics
    • arenaviruses
      • e.g. lassa fever virus
    • reoviruses
      • e.g. rotavirus


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