The features identified in caliciviral TURBS suggest a model for termination-reinitiation in which post-termination 40S subunits are tethered to the mRNA through interactions between the mRNA (through motif 1) and 18S rRNA, initiation factors are recruited and the AUG restart codon located, processes which may require precise RNA folding (involving motif 2) within the TURBS. The TURBS is not highly active as an IRES and 40S subunit recruitment probably requires high local 40S subunit concentrations [17, 18] . An important question, therefore, is how the interaction between TURBS motif 1 and 18S rRNA helix 26 is facilitated. Analysis of primary and secondary structural features of the BM2 signal has revealed that it contains a short TURBS (of 45 nt) which is largely single-stranded, with motif 1 likely to be located in the apical loop of a metastable stem-loop structure when the ribosome is positioned at the termination codon of the upstream ORF [11] . We have suggested that motif 1 may thus be ''presented'' to the solvent-accessible apical loop of helix 26, promoting the interaction and subsequent 40S tethering. However, this hypothesis remains contentious. The paucity of stable RNA secondary structure within the BM2 TURBS [11] , the TURBS of FCV [I. Brierley, unpublished observations] and the calicivirus murine norovirus (MNV; [20] ), limits the predictive power of RNA folding programs in the assessment of the likely RNA folds present before and after ribosomal transit through the TURBS. It is also known that eukaryotic initiation factor 3 (eIF3) plays a role in the termination-reinitiation process, perhaps interacting with the TURBS to provide another link between mRNA and the 40S subunit [17] .