Independent expression of avian sarcoma virus in doubly infected chicken embryo fibroblasts.

Infection of a chicken cell with avian sarcoma virus requires division of the infected cell before synthesis of infectious progeny is initiated. This requirement for a cell division for the complete expression of avian sarcoma virus has been examined further with chicken embryo fibroblasts infected with two distinct viruses. Chicken cells infected with and producing a mutant of Rous sarcoma virus temperature sensitive for transformation (tsLA24PR-A) were arrested in G0 by depletion of serum factors from growth medium. These stationary cells continued to produce infectious progeny in the absence of further cell division. Superinfection of the stationary cells with the wild-type Prague strain of Rous sarcoma virus (PR-RSV-C) produced a stable double infection in these cells. Progeny of the superinfecting PR-RSV-C, however, were not detected until these cells underwent division after stimulation with fresh serum-containing medium. The addition of colchicine to these serum-stimulated cells, although not affecting production of the tsLA24PR-A, inhibited the appearance of progeny of the superinfecting PR-RSV-C. These experiments indicate that each avian sarcoma virus infection of a chicken embryo fibroblast requires division of the infected cell for production of that virus regardless of whether or not the cell is already producing a similar virus. The results suggest, therefore, that the requirement for a cell division represents a requirement for an event that controls virus expression in a "cis-acting" fashion specific for the provirus.