Abstract
We have examined the extent of tyrosine phosphorylation of talin, a component of the cytoskeleton localized in the focal adhesions and, therefore, a potential substrate of p60v-src, the transforming protein of Rous sarcoma virus. p60v-src is a tyrosine kinase that induces high levels of phosphotyrosine and the disorganization of the cytoskeleton in transformed cells. With a polyclonal antibody utilized in a previous study [Maher, P. A., Pasquale, E. B., Wang, J. Y. J. & Singer, S. J. (1985) Proc. Natl. Acad. Sci. USA 82, 6576-6580] for the detection of tyrosine-phosphorylated proteins, we have detected phosphotyrosine residues in talin molecules immunoprecipitated from Rous sarcoma virus-transformed, but not normal, chicken embryo fibroblasts. Phospho amino acid analysis of talin from the infected cells confirmed the presence of phosphotyrosine, in addition to phosphoserine and phosphothreonine. The extent of tyrosine modification in talin was compared to that in vinculin, the other focal adhesion component previously found to contain enhanced levels of phosphotyrosine in various retrovirus-transformed cells. A considerably (3 times) larger fraction of the talin than of the vinculin molecules was found to be phosphorylated on tyrosine. The phosphorylation of talin on tyrosine may be crucial for the expression of the abnormal morphology characteristic of cells transformed by Rous sarcoma virus.