Increased phosphorylation of tyrosine in vinculin does not occur upon transformation by some avian sarcoma viruses

The level of phosphotyrosine in vinculin was determined in chicken embryo fibroblasts transformed by various strains of avian sarcoma virus. As previously reported (Sefton et al., Cell 24:165-174, 1981), vinculin was phosphorylated at tyrosine residues in most cultures examined, but the level varied greatly and no detectable change was found in cultures infected with Fujinami sarcoma virus or UR2 sarcoma virus. Regardless of the level of vinculin phosphorylation, the number of organized microfilament bundles was found to be decreased in all transformed cells. These results strongly suggest that tyrosine phosphorylation of vinculin is not an obligatory step in cell transformation by this class of oncogenes, nor is it correlated with the associated cytoskeletal disarray.