Replication of human cytomegalovirus DNA: lack of dependence on cell DNA synthesis

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Abstract
Human cytomegalovirus (CMV) DNA synthesis was studied in 5-fluorouracil (FU)-treated and untreated human embryonic lung cells, which differ greatly with respect to the number of cells in the culture synthesizing cellular DNA. CMV DNA synthesis proceeded at the same rate in FU-treated and in untreated cells. CMV infection also reversed the inhibitory effects of FU and activated cellular DNA synthesis in some of the cells in the FU-treated culture. Autoradiographic studies showed that more than 20% of the cells in the infected FU-treated culture synthesized viral DNA when less than 1% had synthesized cellular DNA, indicating that the synthesis of viral macromolecules proceeds in cells that do not synthesize cellular DNA from the time of infection, and that viral DNA synthesis proceeds independently of the host cell DNA synthesis. Combined autoradiographic and immunofluorescence studies of both the FU-treated and untreated infected cells showed that, whereas 20% of the cells in the cultures synthesize viral DNA and viral antigens, only about 3 to 6% of those cells that synthesize cellular DNA also synthesize viral antigen. Thus, productive infection was delayed or inhibited in those cells that were stimulated by CMV infection to synthesize cellular DNA.