Notes on Genus: Spumavirus

enveloped spheres
enveloped spheres

Type member: Simian foamy virus 1


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 more than 10 kb, and because they infect mammals.


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


A dimer of linear, positive sense, ssRNA molecules, each 10.5-13.5 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 other regulatory genes are encoded at the 3'-end of the genome. The pro and the pol are translated from a single spliced mRNA and the other genes downstream are translated from separate spliced mRNAs.

Type Member Genomic Organization

The major genes are
  1. gag: structural polyprotein of 70.7 kDa
  2. pro: protease
  3. pol: polyprotein (pro-pol of 129.9 kDa)
  4. env: envelope proteins (113.3 kDa)
  5. taf: transactivating factor of 33.8 kDa
  6. bet: > 48 kDa