Cellular replication and the persistence of inducible RNA type C viruses

Cells of mouse and rat origin contain endogenous type C viruses. There are intrinsic regulatory factors which restrict the ability of different classes of these inducible viruses to persist in cells after chemical activation. The cellular block to certain viruses is shown to be overcome under conditions in which the virus-activated cells are allowed continued exponential growth. These findings may help to explain the high frequency at which replicating type C viruses are detectable in naturally occurring tumors of some species.