Defective interfering particles of coronavirus.

Abstract

Defective interfering (DI) particles are viral deletion mutants, which cannot replicate by themselves and require homologous standard viruses to provide helper functions for their replication. DI particles also interfere with the replication of helper virus. Many studies have suggested a role for DI particles in evolution, persistent infection and pathogenesis of various viruses. Although coronaviruses readily establish persistent infection in vitro and in vivo, there have been no reports of isolation of coronavirus DI particles during persistent infection. We have, however, detected the generation of coronavirus DI particles during high-multiplicity passages of the JHM strain of MHV in tissue culture (Makino et al., 1984a). These DI particles contain a single-stranded RNA genome of roughly 5.2 × 106 molecular weight which is slightly smaller than the genome of the standard virus (M.W. 5.4 × 106). Oligonucleotide fingerprinting studies showed that the RNA of JHM DI is missing several large RNase T1-resistant oligonucleotides, which represent several different regions on the standard viral genome (Makino et al., 1984a; 1984b). This observation suggests that the coronavirus DI particles are unique since the DI genomes of other viruses usually exhibit more extensive deletions. Additionally, coronavirus DIs interfere with the replication of the standard virus to a much smaller extent. We have further shown that, with the exception of mRNA 7, the synthesis of the virus-specific mRNAs in DI-infected cells is inhibited. Instead, the infected cells contain two novel RNA species: one is the DI-specific genomic RNA (DIssA), which is eventually incorporated into the virus particles, the other novel RNA species is subgenomic but of variable size, depending on the level of DI passage. This subgenomic RNA is single-stranded, polyadenylated and contains sequences derived from various noncontiguous parts of the DI genome (Makino et al., 1985). In this report, we present data on the possible mechanisms of synthesis of the two DI-specific RNA species.KeywordsHelper VirusReplicative IntermediateMouse Hepatitis VirusHelper FunctionVirus DilutionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.