Notes on Genus: Gammaretrovirus

enveloped spheres
enveloped spheres

Type member: Murine leukemia virus


General Description

This is one of the genera in the family Retroviridae. Fully-functional members are distinguished from those of the other genera by the presence of only 4 ORFs and a genome of more than 8 kb.


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


A dimer of linear, positive sense, ssRNA molecules, each 8-9 kb long and with a 3'-polyA tail.

Genus Genomic Organization

Fully functional species contain 4 genes (gag, pro, pol and env) which are cleaved into the mature proteins. A spliced mRNA is used to generate the env, while the pro and pol are translated after readthrough of the gag stop codon.

Type Member Genomic Organization

The four major genes are
  1. gag: structural polyprotein of 60.8 kDa, consisting of MA (14.7 kDa), pp12 (8.7 kDa), CA (30.6kDa) and NC (6.4 kDa)
  2. pro: protease of 13.6 kDa
  3. pol: polyprotein of 121.0 kDa containing the reverse transcriptase (RT, 74.7 kDa) and integrase (IN, 46.3 kDa)
  4. env: envelope proteins, consisting of surface protein (SU, 47.9 kDa) and transmembrane protein (TM, 21.8 kDa)