Abstract: | Actinomycin D, known for its suppression of cellular RNA synthesis and for the reduction of the rate of synthesis of double-stranded DNA by the RNA tumor virus RNA-dependent DNA polymerase, was found to interact with single-stranded DNA in such a way as to inhibit DNA . DNA and DNA . RNA hybridizations. This finding is discussed in the light of the observation that DNA elongation during DNA synthesis of RNA tumor viruses is blocked in vitro in the presence of actinomycin D. It thus supports the model that hybridization is a necessary step during RNA tumor virus DNA synthesis. |