Stimulation of DNA Synthesis in Resting Stage Human Fibroblasts after Infection with Rous Sarcoma Virus

ROUS sarcoma virus (RSV) suspensions can induce the synthesis of deoxyribonucleic acid (DNA) and mitosis in resting stage human fibroblasts1. The virus can also induce DNA synthesis in undividing myotubes2and DNA synthesis and mitosis in resting stage chick embryo fibroblasts3,4. The stimulatory activity may not be identifiable with the virus particle, for when the virus suspension was treated with RSV anti-serum the focus forming capacity was inhibited but the stimulatory action was not eliminated1. We have now extended these findings. The WI-38 human embryonic line5was used maintained in Eagle's minimal essential medium6supplemented with 10 per cent calf serum and aureomycin (50 µg/ml.). RSV suspensions were obtained from the supernatants of infected chick embryo fibroblastic cultures, and had a titre of 105FFU/ml. DNA synthesis was estimated by adding 0.1 µCi/ml. of labelled thymidine (3H-TdR) (specific activity, 14 Ci/mmole) to the cultures. The cells were fixed 24 h later, DNA was extracted7and the radioactivity incorporated was measured in a liquid scintillation counter.