FIG. 7.

A model of RNA template-selection and recruitment by the p33 replicase protein in Tombusviruses. First, p33 and a smaller amount of p92 are being synthesized by the ribosome by using the gRNA. Second, p33, likely together with other p33 and/or p92 molecules, binds specifically to RII(+)-SL in the gRNA. Heterologous viral and host RNAs lacking RII(+)-SL will not be selected, resulting in replication of only the cognate RNA. We predict that in order to allow sufficient translation, production of a threshold level of p33 is needed prior to recruitment of the gRNA into replication. Third, stably associated RNA:p33 complex, possibly together with p92 and host factors, is transported to the site of replication (peroxisome-derived membranes [29]). This is predicted to lead to the formation of replication complexes (not shown).