Notes on Family: Retroviridae

enveloped spheres
enveloped spheres

Contents

General Description

This family contains viruses of animals that have an RNA genome but which synthesise DNA copies (by reverse transcription) as replicative intermediates. The virus genomes also integrate into that of their hosts.

Morphology

Virions are spherical and enveloped, 80-100 nm in diameter, with suface projections of glycoprotein.

Genomen

A dimer of linear, positive sense, ssRNA molecules, each 7-11 kb long and with a 3'-polyA tail. All fully-functional members encode 4 major proteins in the same order and which are then processed into the functional, mature, proteins:
  • gag: 3-6 structural non-glycosylated proteins
  • pro: protease
  • pol: polyprotein, including the reverse transcriptase (RT) and integrase (IN)
  • env: two envelope proteins, the SU (surface protein) and TM (transmembrane protein)
In some genera, additional proteins are also encoded.

Genera in the Family

  • Alpharetrovirus: 4 ORFs, genomes <8 kb
  • Betaretrovirus: More than 4 ORFs, genomes not more than 10 kb. Virions assemble as intracytoplasmic particles
  • Gammaretrovirus: 4 ORFs, genomes >8 kb
  • Deltaretrovirus: More than 4 ORFs, genomes not more than 10 kb. Virions assemble at cell membrane. Virion morphology type C
  • Epsilonretrovirus: More than 4 ORFs, genomes >10 kb, infect fish
  • Lentivirus: More than 4 ORFs, genomes not more than 10 kb. Virions assemble at cell membrane. Virions with bar-shaped or concentric core
  • Spumavirus: More than 4 ORFs, genomes >10 kb, infect mammals