Project Title: 13. Molecular and Cellular Radiobiology The Chemistry and Function of DNA Polymerases RX-03-02- (a) Publications: None 14, Scope: A) 200 Word Summary: Enzymes which copy the RNA strand of synthetic RNA:DNA hybrid polymers occur in many animal tissues, although the copying of the RNA strand of a naturally occurring hybrid has not been observed. A primary goal is to determine what role RNA directed DNA synthesis plays in the life cycle of the animal cell. The attempris to isolate in pure form and to characterize an enzyme with this activity from chick embryo tissues, in which it is relatively abundant; also co determine where, within the cell, the enzyme occurs naturally and how the amount of the enzyme may vary during the reproductive cycle of the cell. Synchronized HeLa cells in culture are used in the latter study. A search for a naturally-derived hybrid RNA:DNA polymer which will serve as template for the enzyme is also proposed. Effort is also directed at the question of whether or not the induction of tumors by radiation is effected by ummasking of a virus, Radiation or dibenzanthracene-induced mammary tumors in rats, and the milk of lactating rats bearing such tumors, will be examined for the presence of “reverse transcriptase'’ and/or a virus-like particle. The rats might prove a useful model for similar tamors in humans. B) ‘ Supplement to 200 Word Summary: Some enzymes which synthesize DNA (DNA polymerases) can use RNA templates. In 1970 Temin and Mizutani and Baltimore showed that oncogenic RNA viruses contain an enzyme which will form a DNA chain complementary to template viral RNA, When Spiegelman and co-workers reported that the synthetic polynucleotide hybrid polyriboadenylic acid-polydeoxyribothymidylic acid (rA-dT) is a much more sensitive template-primer for the viral enzymes than is viral RNA, it seemed thac a simple test was available for the detection of oncogenic RNA viruses in tissues, However, certain tissue DNA polymerases can also use this Thus the ability template-primer very effectively under the proper conditions. to incorporate radioactive thymidine phosphate into acid-insoluble polymers in the presence of rA-dT template is no proof of the existence of a virus in e. Methods have been developed during the past year for distinguishthe t ing among : Ker an enzyme is of viral or tissue origin based on its preferences ral synthetic polynucleotide templates. The advancage of RNA-directed DNA synthesis to an RNA Cumor virus is The suggestion has obvious, but what purpose does it serve in normal cells? been made that information transfer from RNA to DNA by enzymes of this type Evidence may play a role in cell differentiation or in gene amplification, suggesting that this might be true has been obtained in the case of the amplification of the genes for ribosomal RNA which takes place during the (See Continuation Sheet) 11792171 RX-217