Interactions between Brome Mosaic Virus RNAs and Cytoplasmic Processing Bodies

Abstract

Cytoplasmic processing bodies are sites where nontranslating mRNAs accumulate for different fates, including decapping and degradation, storage, or returning to translation. Previous work has also shown that the Lsm1-7p complex, Dhh1p, and Pat1p, which are all components of P bodies, are required for translation and subsequent recruitment to replication of the plant virus brome mosaic virus (BMV) genomic RNAs when replication is reproduced in yeast cells. To better understand the role of P bodies in BMV replication, we examined the subcellular locations of BMV RNAs in yeast cells. We observed that BMV genomic RNA2 and RNA3 accumulated in P bodies in a manner dependent on cis-acting RNA replication signals, which also directed nonviral RNAs to P bodies. Furthermore, the viral RNA-dependent RNA polymerase coimmunoprecipitates and shows partial colocalization with the P-body component Lsm1p. These observations suggest that the accumulation of BMV RNAs in P bodies may be an important step in RNA replication complex assembly for BMV, and possibly for other positive-strand RNA viruses.The life cycle of viruses in eukaryotic cells requires that the virus complete its life cycle in the context of the host physiology. One interesting aspect of this process is how important steps in viral replication and packaging interface with translation. Since positive-strand RNA viruses, double-stranded RNA viruses, and reverse-transcribing viruses use the same viral genomic RNA as substrates for translation, encapsidation, and replication, mechanisms are required to segregate packaging and replicative events away from translation of the RNAs, thereby avoiding competition between elongating ribosomes and the packaging or replicative machineries. Although they are of significant importance to the viral replicative process, the mechanisms by which viruses segregate translation from replication and assembly are not well understood.One class of viruses in which the interplay between translation and replication is important is the positive-strand RNA viruses, which encompass over one-third of all virus genera and include numerous well-known pathogens, such as hepatitis C virus and West Nile virus. Despite their differences, all positive-strand RNA viruses share similar life cycles. Following infection, the positive-strand RNA first serves as mRNA to produce viral replication factors, and then the transcript exits translation and is selectively recruited to a membrane-associated replication complex (27). An unresolved issue is the mechanism(s) bringing the viral RNAs and proteins together and thus facilitating the assembly of these replication complexes.Insight into the host factors required for the assembly of replication complexes has come from the study of brome mosaic virus (BMV), which has a tripartite segmented genome consisting of RNA1, RNA2, and RNA3 and normally infects plants. Viral RNA replication requires the RNA-dependent RNA polymerase (RdRp), encoded by RNA2, and the 1a protein, which is encoded by RNA1 and functions in the ...

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