Phosphotyrosine-containing proteins and expression of transformation parameters in cells infected with partial transformation mutants of Rous sarcoma virus

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Abstract
We have examined the phosphorylation state of five proteins known to become phosphorylated on tyrosine during transformation by Rous sarcoma virus by using cells infected with a panel of partially transforming mutant viruses. Situations of viral mutant and growth temperature were found in which phosphorylation of some proteins occurred more extensively than that of others, indicating that mutations in the src gene had affected the specificity of pp60src for some of its substrates as well as affecting the activity of the enzyme. To obtain insight into the biological functions of these phosphorylations, comparisons were made between the degree of phosphorylation of these proteins and the expression of various indicators of the transformed phenotype. The data suggest that phosphorylation of proteins l, p, and q (Mr of 46,000, 39,000 and 28,000, respectively) is not sufficient to induce changes in adhesiveness, hexose transport or morphology. The phosphorylation of protein p or l or total phosphotyrosine content correlated well with the production of plasminogen activator, and the phosphorylation of proteins l and q correlated well with increased hexose transport. However, even when good correlations were observed, significant exceptions were sometimes noted. It thus remains possible that some phosphorylations on tyrosine observed in Rous sarcoma virus-transformed cells are not causally related to the expression of the measured parameters of transformation.