Early DNA-RNA Complex from the Endogenous RNA-directed DNA Polymerase Activity of Uninfected Chicken Embryos

Abstract

WHEN endogenous DNA polymerase activity was isolated from normal uninfected chicken embryos1, we suggested that it was RNA-directed for several reasons. The activity was sensitive to RNAase, but was completely resistant to DNAase and partially resistant to actinomycin D; and the DNA product of the chicken endogenous DNA polymerase activity hybridized to RNA isolated from the same fraction from chicken embryos. Both the template and the DNA polymerase of this chicken endogenous DNA polymerase activity were unrelated to the RNAs and DNA polymerases of Rous sarcoma or reticulo-endotheliosis viruses. Further characterization of the RNA tumour virus endogenous DNA polymerase activity as RNA-directed came from the isolation of a complex of RNA and early DNA product2–5. This complex sedimented rapidly in sucrose gradients and banded at the density of RNA and RNA-DNA hybrids in Cs2SO4 equilibrium density gradients. The complex was disrupted by RNAase (which breaks down RNA), alkali (which breaks down RNA and denatures DNA) and heat (which denatures DNA and RNA-DNA hybrids, but leaves intact covalently bound RNA-DNA). However, previously we were not able to isolate such a complex from the chicken endogenous DNA polymerase activity.