Fig 10.

Known functions of the cis-acting replication elements in TBSV plus-strand RNA. Since RII(+)-SL could not be replaced by a heterologous RNA recruitment element, we propose that RII(+)-SL not only is needed for RNA recruitment into replication but also is required for assembly of the replicase complex. The RSE-gPR element is required for assembly of the replicase and also determination of the template for the replicase, since only RNAs which carry the RSE element are used as templates by the TBSV replicase. We propose that the role of UL-DL is not only to bring the RII(+)-SL and RSE-gPR elements into close proximity but also to ensure their proper orientation for replicase assembly.