Mechanism of Carcinogenesis by RNA Tumour Viruses: The RNA- and DNA-dependent DNA Polymerase Activities of Feline Sarcoma Virus

SUMMARY In the absence of added template, the DNA polymerase of the feline sarcoma virus particle appeared to exhibit two-phase kinetics—a rapid reaction for about 4 min., followed by a slower reaction. Equilibrium sedimentation in Cs2SO4 density gradients showed the formation of RNA-DNA complexes within 12 sec., followed by the formation of DNA free of an RNA template. Virtually all of the DNA product formed at 4 min. and later was free of RNA template. About half of the 60 min. DNA product was double-stranded, since it was resistant to digestion by exonuclease I and eluted from hydroxyapatite columns at the salt concentration characteristic for duplex DNA. After denaturation, the 15, 30 and 60 min. DNA product sedimented at 6s and formed a broad band in CsCl gradients with an average buoyant density of about 1.725. Calf thymus DNA stimulated DNA polymerase activity of detergent-treated virus particle about 10- to 20-fold, indicating the presence of DNA-dependent as well as RNA-dependent DNA polymerase activity within the virus particle.