Transcription of the genomes of type 1 and type 3 reoviruses.

The double-stranded ribonucleic acid (RNA) genome of type 1 reovirus was fragmented into three size classes on extraction, as has already been shown for reovirus type 3. The relative amounts and molecular weights of the three classes were the same for the two viruses. Cells infected with type 1 virus synthesized three classes of messenger RNA. Each class of messenger RNA hybridized exclusively with a denatured double-stranded RNA fragment of equivalent length, as had also been found for type 3 reovirus. The double-stranded RNA segments thus act as specific units for transcription of messenger RNA in the infected cells. In cells infected with type 3 reovirus, the three classes of messenger RNA are made in equal amounts throughout the course of multiplication. In contrast, cells infected with type 1 virus produced only half as much of the largest messenger RNA as they did of the other two classes at all times during the replicative cycle. This finding suggests that transcription of the largest segments of type 1 viral genome is restricted.