Characterization of the viral inhibitory factor (VIF) demonstrable in adenovirus-induced tumor and transformed cells: I. Effect on DNA and viral capsid protein synthesis

Abstract

The mode of action of the viral inhibitory factor (VIF) demonstrated in homogenates of type 12 adenovirus (Ad12)-induced hamster tumor cells has been further characterized with respect to its effect on synthesis of type 2 adenovirus (Ad2) DNA and capsid proteins. The overall rate of DNA synthesis in infected cells was reduced in the presence of the inhibitor, and analysis by alkaline sucrose gradient centrifugation confirmed that viral DNA synthesis was markedly reduced. It was found, in addition, that the rate of uninfected cell DNA synthesis was reduced by the tumor cell extracts but, because of the complexity of the cell homogenate, it is not known whether the same factor is responsible for inhibition of both viral and cellular DNA synthesis. Virus capsid antigens, as detected by immunofluorescence, were delayed in their appearance in VIF-treated, Ad2-infected cells, but none was completely missing. Acrylamide-gel electrophoresis confirmed that all peptides were synthesized but at a greatly reduced rate. These results are consistent with the observation of reduced viral DNA synthesis and suggest that: (i) VIF acts either on DNA replication itself or at a step in replication prior to DNA synthesis; (ii) whatever the primary site of action, the inhibition is not complete but permits reduced virus replication in all VIF-treated cells, rather than totally eliminating it in some cells.