TRANSFORMATION BY AVIAN-SARCOMA VIRUSES LEADS TO PHOSPHORYLATION OF MULTIPLE CELLULAR PROTEINS ON TYROSINE RESIDUES

Phosphoamino acid compositions were determined for 10 size classes of cellular proteins, separated by electrophoresis through 1-dimensional sodium dodecyl sulfate-polyacrylamide gels. Phosphotyrosine-containing proteins were observed in uninfected chicken embryo fibroblasts in every size class analyzed, ranging from .apprx. 20,000 (20 K) to > 200 K. Transformation of chicken embryo fibroblasts by Rous sarcoma virus or PRC II avian sarcoma virus led to increases in phosphorylation of proteins at tyrosine residues in all of these size classes. A large fraction of the phosphotyrosine-containing protein molecules observed in Rous sarcoma virus-transformed cells was > 100 K with a 2nd broad peak in the 35-60 K range. There apparently are a number of substrates of viral or cellular tyrosine-specific protein kinases which have not yet been identified by other methods.