Defective RNAs in mosquito cells persistently infected with Bunyamwera virus

Viral protein and RNA synthesis were compared in BHK and Aedes albopictus C6/36 (mosquito) cells infected with Bunyamwera virus. In BHK cells host protein synthesis was inhibited and viral proteins were detected until the cells died; in C6/36 cells there was little inhibition of host proteins and viral proteins could not be detected after 36 h post-infection. Relatively more S segment RNA than L or M segment RNA was produced in infected C6/36 cells compared to BHK cells. A persistent infection of C6/36 cells was established and the cells were passaged at weekly intervals for over a year. The titre of virus released from the cells and the level of viral RNA in the cells at different passages fluctuated markedly, but there was no simple relationship between virus titre and the amount of viral RNA. Northern blot analysis of viral RNA extracted from persistently infected cells revealed the presence of subgenomic RNAs derived from the L RNA segment. These defective RNAs were not packaged into nucleocapsids. The presence of the defective RNAs did not correlate with resistance of cells cloned from the persistently infected population to superinfection with homologous virus. Hence the role of these defective RNAs in the maintenance of the persistent state remains to be elucidated.