Notes on Genus: Alpharetrovirus

enveloped spheres
enveloped spheres

Type member: Avian leukosis 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 less than 8 kb. Some species incorporate oncogenes and others are replication defective, with variable deletions in the gag, pol and env genes.


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


A dimer of linear, positive sense, ssRNA molecules, each about 7 kb long (without any oncogene) 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 and frameshifting is used in the generation of the pol.

Type Member Genomic Organization

The four major genes are
  1. gag: structural polyprotein of 74.6 kDa
  2. pro: protease of 13.6 kDa
  3. pol: polyprotein of 98.6 kDa containing the reverse transcriptase (RT, 62.9 kDa) and integrase (IN, 35.7 kDa)
  4. env: envelope proteins, consisting of surface protein (SU, 37.2 kDa) and transmembrane protein (TM, 22.3 kDa)