Intracellular conversion of the RNA of sindbis virus to a double-stranded form

A simple procedure for the preparation of Sindbis virus labeled with uridine-³H was devised. The product was radiochemically pure by several criteria. During the first hour of infection some of the RNA of this labeled virus was found in a more slowly sedimenting form that was resistant to RNase and had other properties of double-stranded RNA. This conversion of parental viral RNA to a double-stranded form was not seen when protein synthesis was inhibited. A viral mutant with a temperature-sensitive block in viral RNA synthesis likewise showed no conversion of parental viral RNA to a double-stranded form at a nonpermissive temperature.