Murine cytomegalovirus DNA synthesis in nuclear monolayers.

Nuclear monolayers of murine cytomegalovirus (MCMV)-infected 3T3 cells were examined for their ability to synthesize viral DNA. Infected S-phase and Go-phase nuclei incorporated more ³H-dTMP than did their uninfected counterparts, although the kinetics of incorporation were similar. Synthesis continued for at least 60 min at 37°. The majority of the viral DNA product (from S-phase nuclei) had a molecular weight of approximately 17 × 10⁶, about one-eighth genome size. Infected nuclei contained a new DNA-polymerase activity, which was stimulated by ammonium sulfate and specifically inhibited by antibodies to infected cell proteins. Although infected Go-phase nuclei also contained this new enzyme activity, they could not synthesize viral DNA, thus reflecting their inability to replicate MCMV-DNA in whole cells.