BSC 422 Lecture Notes - Lecture 15: Rous Sarcoma Virus, Oncogene, Retrovirus
22 May 2018
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Proto-Oncogene:
It is well-established that oncogenic virus contains a relatively small number of
genes which has facilitated the identification of the viral genes that cause cell to
become malignant. The first cancer-causing gene to be identified occurs in Rous
sarcoma virus, a small retrovirus that produces sarcomas in chickens.
An unexpected feature of retroviral oncogene is their lack of involvement in virus
replication while other viral gene involves efficiently in the same process.
Again, the existence of viral oncogene is not an integral part of the virus life cycle.
Therefore, the origin and existence of viral oncogene leads to a new line of
investigation. Such investigations have led to the surprising discovery that the src
gene is not present only in cancer cells.
Using nucleic acid hybridisation techniques, it has been shown that DNA
sequence that Eire homologous to— but not identical with—the Rous src gene can
be detected in the genome of normal cells of a wide variety of organisms
including salmon, mice, cows, birds and humans.
The unexpected discovery that cells contain DNA sequences that are closely
related to viral oncogenes has been substantiated by studies on a variety of other
tumour viruses and, in each case, they resemble genes present in the genome of
normal cell.
The term proto- oncogene has been introduced to refer to these normal cellular
genes that closely resemble oncogenes. The resemblance of viral oncogenes to
proto-oncogene suggests that viral oncogenes may have originally been derived
from normal cellular genes.
According to this concept, the first step in the creation of retro-viral oncogenes
took place million years ago when the ancient virus infected cells and became
integrated in the host chromosomal DNA adjacent to normal cellular proto-
oncogenes.
When the integrated pro-viral DNA was later transcribed to regenerate new viral
RNA molecules, the adjacent proto-oncogene sequences might have been
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Document Summary
It is well-established that oncogenic virus contains a relatively small number of genes which has facilitated the identification of the viral genes that cause cell to become malignant. The first cancer-causing gene to be identified occurs in rous sarcoma virus, a small retrovirus that produces sarcomas in chickens. An unexpected feature of retroviral oncogene is their lack of involvement in virus replication while other viral gene involves efficiently in the same process. Again, the existence of viral oncogene is not an integral part of the virus life cycle. Therefore, the origin and existence of viral oncogene leads to a new line of investigation. Such investigations have led to the surprising discovery that the src gene is not present only in cancer cells. The term proto- oncogene has been introduced to refer to these normal cellular genes that closely resemble oncogenes. The resemblance of viral oncogenes to proto-oncogene suggests that viral oncogenes may have originally been derived from normal cellular genes.
