Figure 2.

RNA replication for (+)ssRNA viruses and PS-mediated packaging. (A) Insertion of turnip crinkle virus (TCV) PS into tomato bushy stunt virus (TBSV) gRNA is sufficient for TCV capsid protein to package the TBSV RNA in protoplast and in the presence of the wild-type TCV gRNA. (B) In viruses such as Togaviruses, the sgRNA and the (−)ssRNA, which are in excess with respect to the gRNA, are not packaged. This is most commonly attributed to presence of a PS. For example, insertion of the Venezuelan equine encephalitis PS in its sgRNA is sufficient to package this RNA molecule. ORF refers to open reading frame.