The relationship between replication of simian virus 40 (SV40) DNA and the various periods of the host-cell cycle was investigated in synchronized CV1 cells. Cells synchronized through a double excess thymidine procedure were infected with SV40 at the beginning or the middle of S, or in G2. The first viral progeny DNA molecules were in all instances detected approximately 20 h after release from the thymidine block, independent of the time of infection. The length of the early, prereplicative

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... ase of the virus growth cycle therefore depended upon the period of the cell cycle at which the cells were infected. Infection with SV40 was also performed on cells obtained in early G1 through selective detachment of cells in metaphase. As long as the cells were in G, at the time of infection, the first cubated under 5 ml of MCV, supplemented with 5% calf serum, antibiotics, and 10-' M deoxyadenosine, 99 on May 9, 2020 by guest