Dependence of Moloney murine leukemia virus production on cell growth.

Production of Moloney murine leukemia virus (MuLV) ceases in cultures of infected mouse fibroblasts made stationary by growth in limiting medium. Stimulation of the cells to reenter the growth cycle synchronously was followed by two waves of virus release. The first wave, occurring within 4 hr after the cells were released from G₀, was unaffected by 0.1 μg/ml of actinomycin D. The second wave, coinciding roughly with the mitotic period of the following cell cycle, was prevented by actinomycin D. Both waves of virus release were inhibited by 10 μg/ml of cycloheximide. The first wave of released virus appears to contain viral RNA already present in the resting cells, while the second wave of released virus particles carry newly formed viral RNA.