dsDNA made by RNase-sensitive DNA polymerase from RSV-transformed cells

THE hypothesis that the RNA-directed DNA polymerase (reverse transcriptase) may function in normal cells¹ as part of the machinery for gene amplification is being investigated^2-8. Cytoplasmic fractions of normal^6,7,9,10, neoplastic^11-14 and virus-transformed cells^3,15, contain RNase-sensitive DNA polymerase activities. Most studies revealed that cellular DNA polymerases differed greatly from the oncorna virus RNA-directed DNA polymerase^7,9 but the nature of the endogenous template of the cellular DNA polymerases was not described. In view of these findings and reports on the participation of RNA in DNA synthesis by DNA polymerases in bacteria^16-20, and mammalian^21-23 cell systems, we investigated the nature of the template and the role of RNA in the synthesis of DNA by the cytoplasmic RNase-sensitive DNA polymerase activity found in rat cells transformed by the B77 strain of Rous sarcoma virus (R(B77) cells). We found that such preparations contained DNA molecules which served as the template for the RNase-sensitive DNA polymerase activity. We also found that RNA has a function in the synthesis of DNA since nascent DNA molecules, covalently linked to RNA, were synthesised at the very beginning of the reaction.