This phosphoprotein, required for both the initiation and the maintenance of neoplastic transformation, is a protein kinase that catalyzes the phosphorylation of tyrosine residues in vitro. ATP + L-tyrosyl-[protein] = ADP + H(+) + O-phospho-L-tyrosyl-[protein] The phosphorylated form is termed pp60v-src. Belongs to the protein kinase superfamily. Tyr protein kinase family. SRC subfamily.