tyrosine kinase receptors  

Rous sarcoma tyrosine kinase
   Animal c-Src protein is a tyrosine kinase cell signaling protein that activates other enzymes involved in bone & T-cell development by regulating cell proliferation, differentiation, and apoptosis (cell death).

   v-Src is its mutant form that was spread among chicken by a tumor causing virus, Rous Sarcoma virus, which activates cells to divide uncontrollably and ignore signals to die by phosphorylating all kinds substrates, always.
                                                          The two faces of Src
       (adapted from Young et. al., 2001.)