Transformation Viral genome

FIGURE 8.13 Nonreceptor PTKs. These protein kinases form a large family, and most of them contain SH2 and SH3 domains. Several were originally discovered as transforming genes of a viral genome, hence names such as src or abl, derived from Rous sarcoma virus or Abelson murine leukemia virus, respectively. (Adapted from Hunter, T., Biochem. Soc. Trans., 24(2), 307-327, 1996.)... 

Without making a definite commitment, let us assume the hypothesis that expression of viral DNA is the causative factor in the cell transformation to a cancer state. There is certainly a significant body of experiments indicating that this is true in many mammals, but solid evidence in humans still eludes us. The viral genome, incorporated in the cellular genome, is completely repressed for long periods compared to most cells division times. As in the case of lysogenic bacteria, a wide variety of chemical and physi-... 

Plant transformation is now an experimental tool that can be used on many species a large number of genes, viral genomes, and plant-transposable elements have been transferred to the genomes of species such as potato, tobacco, oilseed rape, and so on. 

The key experiment identifying these DNA sequences as oncogenes was to show that DNA transfection of just this portion of the viral genome, in the context of a eukaryotic expression vector, was sufficient to transform cell lines. 

Part or all of the viral genome becomes linearly inserted into chromosomes of transformed cells. For RNA viruses like Rous sarcoma virus, the viral genome must be converted to double-strand DNA before this insertion can occur. The viral enzyme that synthesizes DNA from a single-strand RNA template is called reverse transcriptase, and viruses containing reverse transcriptase are called retroviruses (see here). 

Assays based on measurements of specialized functions and viral products For viruses that do not form plaques or induce CPE in cell cultures. Determination of virus specific parameters, e.g., hemagglutination and hemadsorption tests, inhibition of cell transformation and immunological tests detecting antiviral antigens in cell cultures. Reduction or inhibition of the synthesis of virus specific polypeptides in infected cell cultures, e.g., viral nucleic acids, viral genome copy numbers or the uptake of radio labeled precursors. 

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