Rous sarcoma virus
is a retrovirus
and is the first oncovirus
to have been described: it causes sarcoma
As with all retroviruses, it reverse transcribes its RNA genome into cDNA before integration into the host DNA.
RSV was discovered in 1911 by Peyton Rous
, working at Rockefeller University
in New York City, by injecting cell free extract of chicken
tumour into healthy Plymouth Rock chickens.
The extract was found to induce oncogenesis
. The tumour was found to be composed of connective tissue (a sarcoma).
Rous was awarded the Nobel Prize for the significance of his discovery in 1966.
Structure and genome
RSV is a class VI enveloped virus with a positive sense RNA genome having a DNA intermediate.
RSV has four genes:
- gag - encodes capsid proteins
- pol - encodes reverse transcriptase
- env - encodes envelope proteins and
- src - encodes a tyrosine kinase that attaches phosphate groups to the amino acid tyrosine in host cell proteins.
The RSV genome has terminal repeats enabling its integration into the host genome and also over expression of RSV genes.
The src gene is oncogenic as it triggers uncontrolled growth in abnormal host cells. It is an acquired gene, found to be present throughout the animal kingdom with high levels of conservation between species.
The src gene was taken up by RSV and incorporated into its genome conferring it with the advantage of being able to stimulate uncontrolled mitosis of host cells, providing abundant cells for fresh infection.
The src gene is not essential for RSV proliferation but it greatly increases virulence when present.