An important question that remains to be resolved is whether there is a role for TURBS RNA secondary structure. We previously proposed that the TURBS may fold into two main configurations, in the first of which (mfold 1) motif 1 is sequestered in a base-paired region [11] , which may explain why it does not have significant IRES activity (as is seen with Gtx [28] [29] [30] ). Translation through and termination at the M1 ORF would remodel mfold 1 to a structure similar to that shown in mfold 2 ( Figure 8B ) such that motif 1 would then be presented to the 18S rRNA on the apical loop of a stem-loop structure. The experiments described in Figure 1 agree well with dependence on a structure similar to that presented in mfold 2, in that the substituted nucleotides in the 6.1 and 6.4 replacement mutants would act to disrupt the stem, whereas substitution of nucleotides in the 6.6 replacement mutants would be expected to have no effect as they would lie within the mRNA channel of the terminating ribosome. However, we also carried out a mutational analysis of the main stem regions present in mfold 1 and mfold 2 but the data did not corroborate our structural predictions. Whilst disruption of either of the putative stems in one arm inhibited reinitiation, little effect was observed when stem formation was disrupted in arm 2 of either stem-loop structure, although some restoration of BM2 synthesis was observed in an mRNA containing a pseudowild-type mfold 2 structure. It should be noted that RNA structure mapping of the TURBS of BM2 [11] , FCV (Brierley et al. unpublished observations) and MNV [20] TURBS reveals that they are largely single-stranded, and probably metastable. It may be that TURBS are able to adopt a variety of conformations, some of which are able to facilitate terminationreinitiation, for example the 6 nt replacement mutant 6.4r2 ( Figure 1B) . Alternatively, the requirement for translation through the TURBS may not be due to a dependence on translational remodelling and 'unzipping' of motif 1 from paired regions, but rather just to place the ribosome in proximity to motif 1 (similar to the case for reinitiation in bacteriophage where the ribosome is placed close to the vestigial Shine-Dalgarno [SD] motif [41] ). It is clear that further work is required to understand the putative role of RNA secondary structure in termination-reinitiation.