Human retroviruses

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Human retroviruses

• Four human retroviruses have been identified. All
  infect CD4 bearing cells. These were only
  identified in the 1980's when it became possible
  to culture T-cells in vitro.
• HTLV1 - T-cell leukaemias/lymphomas
• Tropical spastic paraparesis
• HTLV2 - No known pathology
• HIV 1 2 - AIDS

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(Macrophage).
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• They are enveloped viruses, with an RNA genome.
  The name is derived from the fact that the virus
  particle contains an RNA-dependent DNA Polymerase
  (Reverse transcriptase). This enzyme converts the
  RNA genome into DNA, which then integrates into
  the host chromosomal DNA. The reverse
  transcriptase is highly error prone and rapid
  genetic variation is a feature of this group.

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• The genus is divided into three sub families

Oncovirinae - oncogenic - cause sarcomas and
leukaemias in animals e.g. Rous Sarcoma Virus
Lentivirinae - slow progressive degenerative
disorders e.g. visnavirus of sheep, human
immunodeficiency virus (HIV)
Spumavirinae - no pathology known
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(No Transcript)
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Defective virus

• Virus, which has lost a gene that is essential
  for replication and can, therefore, only undergo
  productive infection if the cell that is
  harboring the virus is superinfected with a
  helper virus that can supply the function of the
  lost gene. Many oncogenic retroviruses are
  defective.

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Genome organization

• The virus has a diploid genome (2 copies of RNA
  genome per virus particle). The genome codes for
  at least three genes gag, pol and env
• gag - codes for the core proteins, structural
  virion components
• pol - reverse transcriptase
• env - envelope glycoprotein

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• LTR -Long terminal repeat - is a regulatory
  sequence at each end of the genome.
• LTR - gag - pol - env LTR
• Their presence allows integration into the host
  chromosome and controls gene expression