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Evidence that there exist four classes of RNA tumor viruses which encode proteins with associated tyrosine protein
Abstract:
The transforming protein of Rous sarcoma virus, p60src, the Abelson virus protein, p120, and the Y73 virus protein, p90, all have associated tyrosine protein kinase activities in vitro. Possible structural homology between these functionally related proteins was investigated by two-dimensional analysis of both methionine-containing and phosphate-containing tryptic peptides derived from biosynthetically labeled proteins. Marked differences were found between the maps of both [35S]methionine-labeled and 32P-labeled tryptic peptides. This suggests that the transforming gene of Rous sarcoma virus and the putative transforming genes of Abelson virus and Y73 virus are different. In addition, each of these genes has been shown previously to be unrelated to the putative transforming gene of Fujinami sarcoma virus, another virus which encodes a protein with associated tyrosine protein kinase activity. Therefore, it appears that there exist at least four distinct classes of functionally related RNA tumor viruses. Analysis of phosphorylated tryptic peptides did, however, reveal homology between one of the two phosphotyrosine-containing tryptic peptides of p90 of Y73 virus and the single phosphotyrosine-containing tryptic peptide of p60src of Rous sarcoma virus. Comigration of these two peptides in several different buffers and the identical mobility of their phosphorylated cleavage products after secondary digestion with protease V8 of Staphylococcus aureus indicated that p60src and p90 contain an identical site of tyrosine phosphorylation in vivo. The results are discussed with respect to the evolution of RNA tumor viruses which encode proteins with associated tyrosine protein kinase activities and the limitations of analysis of detecting homology between genes by both molecular hybridization and peptide mapping.
Insights
Investigating tyrosine protein kinase activities in RNA tumor viruses reveals at least four distinct classes. However, p60src and p90 proteins share an identical tyrosine phosphorylation site, suggesting evolutionary links.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- Several RNA tumor viruses encode proteins with tyrosine protein kinase activity.
- These proteins, including p60src, p120, and p90, are functionally related but their structural homology was unclear.
Purpose of the Study:
- To investigate the structural homology between functionally related tyrosine protein kinase-associated proteins from different RNA tumor viruses.
- To determine the evolutionary relationships between these viruses based on their transforming genes and encoded proteins.
Main Methods:
- Two-dimensional peptide mapping of biosynthetically labeled proteins ([35S]methionine and 32P-phosphate).
- Analysis of tryptic peptides, including phosphotyrosine-containing peptides.
- Secondary digestion with Staphylococcus aureus protease V8.
Main Results:
- Peptide maps showed marked differences, suggesting distinct transforming genes for Rous sarcoma virus, Abelson virus, and Y73 virus.
- These genes are unrelated to Fujinami sarcoma virus transforming gene, indicating at least four distinct viral classes.
- Homology was found between a phosphotyrosine peptide of p90 (Y73 virus) and p60src (Rous sarcoma virus), indicating an identical in vivo tyrosine phosphorylation site.
Conclusions:
- RNA tumor viruses encoding tyrosine protein kinases represent at least four distinct evolutionary classes.
- Despite distinct genes, p60src and p90 share a conserved tyrosine phosphorylation site, hinting at evolutionary convergence or shared ancestry.
- Peptide mapping is a valuable tool for assessing homology and evolutionary relationships among viral proteins, with limitations in detecting subtle gene homologies.