Early chicken embryos that are either positive or negative for group-specific
antigens of avian leukosis viruses contained endogenous
RNA-directed DNA polymerase activity. This endogenous
DNA polymerase activity was not increased after mixture of soluble
DNA polymerases isolated from chicken embryos with disrupted chicken embryo cells. The endogenous activity was resistant to treatment with
deoxyribonuclease, and the initial rate of
DNA synthesis was partially resistant to
actinomycin D. In contrast, over 90% of the endogenous polymerase activity was destroyed by
ribonuclease in medium with high
salt concentration. The
DNA product of the endogenous
DNA polymerase activity from chicken embryos did not hybridize with
RNA of Rous sarcoma virus or reticuloendotheliosis virus, whereas about 40% of this
DNA product hybridized with the
RNA from the same chicken-cell fraction. Antibody against
DNA polymerase of avian myeloblastosis virus did not neutralize the chicken endogenous
DNA polymerase activity. These results demonstrate that uninfected chicken embryo cells contain endogenous
RNA-directed DNA polymerase activity that is not derived from
avian leukosis or
reticuloendotheliosis viruses.