Transcription by infectious subviral particles of reovirus

Digestion of purified reovirus with chymotrypsin in the presence of 0.15 M NaCl converts virions to infectious subviral particles (SVP(i)). The SVP(i) have an active ribonucleic acid (RNA) polymerase and are similar in composition to the partially uncoated virions which have been isolated from infected L cells. SVP(i) have a buoyant density of 1.40 g/ml in CsCl and sediment at 420S as compared to 1.37 g/ml and 630S for virions. They consist of 30% less protein and include the polypeptides of the inner structural layer, lambda(1), lambda(2), and sigma(3), and a polypeptide derived by cleavage of mu(2), a constituent of the outer shell. The genome RNA is retained within SVP(i), but more than 60% of the "adenine-rich," single-stranded RNA is released by the proteolytic treatment. Infection of L cells with SVP(i) or virions results in the transcription of all 10 genome segments. In cycloheximide-treated SVP(i)-infected cells, transcription occurs predominantly from one medium and two small genome segments, the same pattern of early messenger RNA (mRNA) observed in virion-infected cells. In contrast, SVP(i) incubated in vitro synthesize mRNA corresponding to all genome segments.