An abbreviated form of the word sarcoma, the term Src encompasses a family of tyrosine kinases that are proto-oncogenic. Tyrosine kinases are enzymes that are capable of transferring a phosphate group from ATP to a tyrosine residue. The phosphorylation of proteins by tyrosine kinases is critical for signal transduction in multicellular animals. Generally animal cells contain at least one of the Src families of tyrosine kinases. V-Src is the mutated version of cellular Src (C-Src) that has lost its characteristic ability to inhibit enzyme activity. C-Src was targeted in the fox lung cells featured in the digital video sequences presented in this section with mEmerald, while H2B was fluorescently labeled with mCherry.