Stimulation of pp60c‐src tyrosyl kinase activity in polyoma virus–infected mouse cells is closely associated with polyoma middle tumor antigen synthesis

We have examined the effect of polyoma virus infection of primary mouse embryo cells on the tyrosyl kinase activity associated with the cellular src gene product. pp60c‐src. The results of our studies demonstrate that infection of mouse cells with wild‐type polyoma virus or viral mutants capable of transforming rodent cells in culture and inducing tumors in animals results in the stimulation of pp60c‐src tyrosyl kinase activity. The level of pp60c‐src kinase stimulation in infected cells was found to be proportional to both the oncogenic potential of the virus strain used for infection and the characteristic phenotype of rodent cells transformed by the various strains of polyoma virus. Stimulation of pp60c‐src kinase activity was not observed in mouse cells infected with transformation‐defective strains of polyoma virus. In examining the kinetics of pp60c‐src kinase stimulation in mouse cells at various times following wild‐type polyoma virus infection, we found that the level of pp60c‐src kinase activity correlated directly with the synthesis of polyoma virus‐encoded tumor antigens. By comparing wild‐type polyoma virus with other viral mutants in these experiments, we conclude that the stimulation of pp60c‐src kinase activity in mouse cells following polyoma virus infection is associated with the synthesis of middle tumor antigen.