Rous sarcoma virus

Rous sarcoma virus is a retrovirus; a class VI enveloped virus with a positive sense RNA genome having a DNA intermediate. As with all retroviruses, it reverse transcribes its RNA genome into cDNA before integration into the host DNA.

The RSV genome has terminal repeats enabling its integration into the host genome and also over expression of RSV genes.

History
RSV was discovered in 1911 by Peyton Rous, by injecting cell free extract of chicken tumour into healthy chickens.

The extract was found to induce oncogenesis in Plymouth Rock chickens. 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.

Genes
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.

src gene
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 sgrc gene is not essential for RSV proliferation but it greatly increases virulence when present.