Project Title: 14, Scope: Molecular and Cellular Radiobiology The Chemistry and Function of DNA Polymerases RX-03-02- (a) (Cont'd.) presumed to be of tissue rather than viral origin. These studies should enable one to distinguish clearly between "reverse transcriptase" of viral origin and similar tissue-derived enzyme activity. A third research effort is contemplated in collaboration with Dr. Wolf Prensky, Sloan-Kettering Institute. A method of labeling RNA with Iodine-125 developed at Brookhaven National Laboratory Medical Department by Dr. S, L. Commerford, produces RNA with much higher specific activity than attainable by any other method, Dr, Prensky has used this method to study the specific hybridization of (labeled) ribosomal 5S RNA with metaphase chromosomes of drosophila and some other species, locating the genes for 5S RNA by radioautography,. The RNA of oncogenic RNA viruses will be labeled by I-125. ‘Then a radioautographic search will be made for sequences within cellular DNA which are complementary to viral RNA. Cells transformed by the virus as well as non-transformed cells will be studied, and cells transformed by one virus will be studied for complementarity to RNA from other viruses. Although most investigators have found some complementarity between viral RNA and cellular DNA, one cannot be sure from a review of the literature whether the complete viral genome is present in transformed cells. Technically these experiments will be difficult but the collaboration with Dr. Prensky using his automated equipment will significantly increase the sensitivity of the procedure so that one or two grains per cell can be measured, Calculations show that introduction of only one I atom per 100 bases in RNA will give . more than 100 x 106 dpm/ug, which is the highest specific activity attain- able using all four tritium labeled RNA precursors, but nowhere near the maximum possible with I-125. 15, Relationship to Other Projects: Other laboratories studying RNA directed DNA synthesis in chick embryo tissue include those. of Chargaff at Columbia University, Faculte des Sciences, Paris, and Chapeville at Reports from these two laboratories are in conflict and differ from BNL data, Weissbach, at Roche Institute of Molecular Biology has reported on a Similar enzyme (or enzymes?) from HeLa cells. This group is not studying the gwiations in enzyme level with the cell cycle. Their data in part have beemgahown to be in error at BNL. Mammary tumors and viruses in mice, are extensively studied. Whether these studies are relevance to genesis of human breast cancer is uncertain but is studied intensively by Moore, Institute for Medical Research, Camden, New Jersey; and Spiegelman, Columbia University, Chopra, National Cancer Institute, and Shidlovsky, Pfizer, Inc., Maywood, New Jersey, have studied (See Continuation Sheet) (17192174 RX-219