The Virus Vector Core will provide tissue-culture- and animal-derived viruses for all three projects. The core will make and titer stocks of recombinant MMTVs, G-MLVs and hybrid viruses. The core will also maintain and store all tissue culture lines and plasmid/viral DNAs used in all three projects. In conjunction with Core B (Mouse Breeding/Transgenic Core), the Virus Vector Core will also purify and provide mil-borne MMTV stocks for Projects 1 and 2. Dr. Paul Bates will supervise this core Dr. Bates will also make bi-monthly reports to the Executive Committee about new vector technologies that may be of use to the Program.