Oncornavirus‐like particles in HeLa cells. III. Biochemical characterization of the virus

Oncornavirus‐like particles observed and purified from HeLa cell culture supernates have a density in sucrose of 1.16‐1.17 g/cm 3 . They contain DNA polymerase and ribonuclease activities with properties characteristic of reverse transcriptase and ribonuclease H of known oncornaviruses. The DNA polymerase and RNase H are antigenically similar to those of Mason‐Pfizer monkey virus.