Phosphorylations of the Subcellular Matrix in Cells Transformed by ROUS' Sarcoma Virus

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Abstract
The transforming protein of Rous sarcoma virus (RSV) is a phosphoprotein of MW 60,000 (pp60src) which displays protein kinase activity specific for tyrosine residues; pp60src is associated with the plasma membrane and is recovered in the detergent-insoluble material which represents the subcellular matrix of the cell. After phosphorylation of this material of RSV-transformed mouse fibroblast cells with [.gamma.-32P]ATP, 5 phosphoproteins were detected which are not seen in normal cells. These proteins (MW = 135,000, 125,000, 75,000, 70,000, 60,000) contain phosphotyrosine. Their phosphorylation is strongly inhibited by anti-pp60src antibodies. In cells transformed by a temperature-sensitive mutant of RSV, these phosphoproteins, present at the permissive temperature, are no longer detected at the nonpermissive temperature. Evidently these phosphorylations are mediated by pp60src protein kinase activity. This supports a possible role of the phosphorylation of cytoskeletal proteins in the transformation process.