One of the best studied retroviruses infects chicken and is called Rous Sarcoma Virus. The oncogene found in this retrovirus is src. The product of this gene is a protein kinase that phosphorylates tyrosine residues in other proteins. The protein products of other retroviral oncogenes also regulate cell division processes and contain one of four functions. In 1976 Drs. Dominique Stehelin, J. Michael Bishop and Harold E. Varmus of the University of California, San Francisco demonstrated that oncogenes were activated proto-oncogenes, found in many organisms including humans