Figure 3.

Novel uses of RNA decay factors by viruses. In addition to simply stabilizing or destabilizing viral RNAs, the cellular mRNA decay machinery and associated factors are also used by selected viruses to perform a variety of interesting roles in gene expression and replication. (a) Flaviviruses such as West Nile Virus use the cellular exoribonuclease Xrn1 to generate decay intermediates that result in novel subgenomic sfRNA transcripts, which have been shown to influence cytopathology. (b) HCV binds miRNA-122, which is abundant in liver cells, to generate/stabilize the structural elements at the 5′ end of its genomic RNA that are required for efficient viral gene expression/replication. (c) The Nsp14 exonuclease encoded by coronaviruses has been demonstrated to play a role in viral evolution and the generation of quasispecies diversity. (d) Selected transcripts encoded by Borna viruses contain instability elements that reduce the level of expression of specific mRNAs in a post-transcriptional fashion. This affords an additional level of control of gene expression for this RNA virus.