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 S GS1-2 were composed of double-stranded RNA (dsRNA) with an estimated s ize of 400 and 380 bp, respectively. Their segment of origin was ident ified as the SI by hybridization analysis. The subgenomic segments wer e associated with the virus fraction following CsCl density gradient c entrifugation, indicating that they are packaged. The subgenomic segme nts were also shown to be replicated. Therefore, sequence(s) required for replication and packaging are retained. The relative amounts of su bgenomic segments were shown to be inversely proportional to that of t he S1 segment. The presence of subgenomic segments and concurrent redu ction in the relative amount of the S1 segment were found to be direct ly associated with the decrease in infectious titers. These results su ggest that subgenomic segments are responsible for induction of interf erence by specifically competing with the Si segment during replicatio n and/or packaging. The competitive relationship between the subgenomi c segments and the S1 segment implies that segment-specific sequence(s ) or factor(s) are involved in the replication and/or packaging of eac h individual genome segment.