Cell-cycle dependent appearance of murine leukemia-sarcoma virus antigens

Normal rat kidney (NRK) cells, NRK cells infected with Rauscher murine leukemia virus, and NRK cells infected with Kirsten murine sarcoma-leukemia virus (NRK-K) were synchronized by a double thymidine block. At intervals after release from thymidine blockage, the cells were examined for the presence of viral antigens in the cytoplasm and on the cell surface by immunofluorescent microscopy by using goat anti-Rauscher murine leukemia virus and goat anti-Moloney leukemia virus (Tween-ether disrupted) sera. Detection of viral antigens in the cytoplasm was periodic during the cell cycle. Antigens were detected first during the S phase, increased during the G2 phase, and disappeared during the M and G1 phases. A similar pattern of surface immunofluorescence was observed. Infectious virus was detected in culture fluids from synchronized cells during the M phase. Surface immunofluorescence was detected in NRK-K cells with anti-Rauscher murine leukemia virus and may represent the presence of group-specific antigens on the cell surface. Control, uninfected NRK cells, which did not normally fluoresce, showed weak immunofluorescence during the S and G2 phases after synchronization. Synchronization can be used to amplify latent oncornavirus expression.