Figure 3.

The role of RNA replication during RNA packaging. (A) Most RNA-dependent RNA polymerases (RdRp) of (+)ssRNA viruses interact with organelle membranes, creating viral assembly sites or replication factories. Sometimes these sites are very close to the ER. (B) There are viruses in which selective packaging seems to depend only on the ability of an RNA to be replicated by the RdRp (e.g., poliovirus). There is evidence that the ability of an RNA to act as a template for translation contributes to packaging selectivity (e.g., flock house virus). (C) In some other cases, the contribution of RNA replication is not sufficient, and the presence of a PS (red element with an *) is required for selective packaging. For example, in alphaviruses the presence of this signal is key to package only the genomic (blue with the PS in red with an *) but not the subgenomic RNA (orange).