Establishment and maintenance of the interferon-induced antiviral state: studies in enucleated cells.

Requirements for the physical presence of the cell's nucleus for the establishment and maintenance of the interferon-induced antiviral state were investigated. Enucleated chicken embryo fibroblasts were obtained by cytochalasin B treatment during centrifugation. The inhibition of vaccinia virus cytoplasmic DNA synthesis, monitored by autoradiography, was used to measure the antiviral activity resulting from interferon treatment. The antiviral state is not established in cells treated with interferon after removal of their nuclei. On the other hand, cells first treated with interferon for 6 or 12 h and then enucleated express the antiviral state. Furthermore, the antiviral state is maintained in enucleated cells for 16 h after enucleation. The antiviral state appears to be more stable in enucleates than in the residual nucleated cells found in the same cultures. Single cells of antiviral populations are found to be either fully permissive or fully restrictive to vaccinia DNA synthesis. The effect of an increasing intracellular multiplicity of infectious virus is to overcome the antiviral cell's block against viral DNA synthesis.