We have found that a transforming protein pp60src from chick embryo fibroblasts infected with a tumorigenic avian sarcoma virus is located almost entirely in the cytoskeletal framework. Cytoskeletons were prepared by lipid extraction of transformed cells with a mild detergent and the transforming protein recognized by its protein kinase activity, by its precipitation with immune sera from tumor bearing rabbits (TBR) and by the molecular weight (60,000) of the radioactive products on electropherograms. The pp60src of cytoskeletons may also be labeled with (gamma 32P) ATP at a tyrosine site nearest the carboxylterminus. We plan to determine whether a cyclic-AMP dependent phosphorylation of a second serine site at the amino terminus can be catalyzed by the cytoskeleton preparation. A preliminary experiment has indicated that a nuclear fraction contains part of the pp60src. By use of immunofluorescent antisera we will attempt to locate the pp60src within the cytoskeletal framework and in particular within the nucleus. By use of cross linking reagents and 32P-labeled pp60src we will attempt to identify nearest neighbor protein as they occur in the cytoskeleton. These studies should provide evidence concerning possible proteins substrates of the transforming protein.