Notes on Genus: Deltaretrovirus

enveloped spheres
enveloped spheres

Type member: Bovine leukemia virus


General Description

This is one of the genera in the family Retroviridae. Members are distinguished from those of the other genera by the presence of 6 ORFs, a genome of less than 10 kb and because virions assemble at the cell membrane.


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


A dimer of linear, positive sense, ssRNA molecules, each 8.4-9 kb long and with a 3'-polyA tail.

Genus Genomic Organization

In addition to the standard 4 genes of the family (gag, pro, pol and env) two additional genes (rex and tax) at the 3'-end of the genome encode proteins that regulate RNA synthesis and processing. Frameshifting is used to generate the pro and the pol from the same mRNA as the gag. Onespliced mRNAs is used to generate the env gene and a second one for the other two genes.

Type Member Genomic Organization

The six major genes are
  1. gag: structural polyprotein of 43 kDa, consisting of MA (8 kDa), p4 (3 kDa), CA (24 kDa) and NC (8 kDa)
  2. pro: protease of 20 kDa
  3. pol: polyprotein of 94 kDa
  4. env: envelope proteins, consisting of surface protein (SU, 43 kDa) and transmembrane protein (TM, 15 kDa)
  5. rex: 17 kDa
  6. tax: 34 kDa