Subgenomic S1 segments are packaged by avian reovirus defective interfering particles having an S1 segment deletion

Two subgenomic segments derived from the S1 genome segment (SGS1-1 and SGS1-2) were identified in avian reovirus defective interfering (DI) particle preparations having an S1 segment deletion. Both SGS1-1 and SGS1-2 were composed of double-stranded RNA (dsRNA) with an estimated size of 400 and 380 bp, respectively. Their segment of origin was identified as the S1 by hybridization analysis. The subgenomic segments were associated with the virus fraction following CsCl density gradient centrifugation, indicating that they are packaged. The subgenomic segments were also shown to be replicated. Therefore, sequence(s) required for replication and packaging are retained. The relative amounts of subgenomic segments were shown to be inversely proportional to that of the S1 segment. The presence of subgenomic segments and concurrent reduction in the relative amount of the S1 segment were found to be directly associated with the decrease in infectious titers. These results suggest that subgenomic segments are responsible for induction of interference by specifically competing with the S1 segment during replication and/or packaging. The competitive relationship between the subgenomic segments and the S1 segment implies that segment-specific sequence(s) or factor(s) are involved in the replication and/or packaging of each individual genome segment.