Question

Why does rous sarcoma virus induce tumors within days. However, most oncogenic retroviruses induce cancer after months or years. Does it have to do with the presence or absence of the src gene?

Answer 1

The rous sarcoma virus is a retrovirus known as oncogenic virus that is capable of causing cancer. The tumour was a sarcoma of a connective tissue. The genes are encoded in RNA, not DNA and uses reverse transcriptase, a DNA polymerase uses RNA as a template.

When RSV infects a cell , and it's reverse transcriptase synthesizes DNA copies of its genome. These enter into the nucleus of the cell and insert themselves into the host's chromosomes, in order to complete it's life cycle. It is easy to see that a virus have v-src to its genome will have a strong advantage. By stimulating uncontrolled mitosis in its host and it's induces a growing population of tumour cells.

RSV virus has src gene which encodes a tyrosine kinase which attach with phosphate groups to The residues on a variety of host cell proteins. Two important functions are enable the DNA copies and insert into the host's DNA, and act as enhancers. Src is needed to transform these cells and participate in causing the cell containing mutation to become cancerous.

Whenever the DNA of RSV happens to insert itself near the cellular c-src gene of its host, RNA polymerase II transcribe the c-src gene. The c-src would be removed by normal RNA processing, producing a mRNA encoding the four gene. This would then slip into one of the virus particles being assembled. Certain mutations in c-src RSV become oncogenic.