Despite this progress, the occurence and role of RNA secondary structure within viral TURBS is poorly understood. Direct structure probing and mfold analysis indicates that the RNA upstream of the stop-start window is metastable and whilst the secondary structures proposed for FCV [13] , BM2 [19] and MNV (this study) are superficially similar, the largely single-stranded nature of the TURBS weakens these models and their comparison. The insertion of a premature termination codon upstream of the TURBS blocks reinitiation, ruling out the possibility that VP2 expression occurs by ribosome recruitment to a conventional, structured, viral IRES or by shunting from the untranslated region of the upstream ORF. The requirement for translation through the TURBS may simply reflect the need to deliver ribosomes to the stop-start window, but it could also indicate a requirement to remodel the TURBS, conceivably by alteration of RNA secondary structure or displacement of a bound factor. Based on chemical and enzymatic RNA structure probing of the BM2 signal and folding predictions (mfold), it has been suggested that transit of the ribosome to the stop-start window leads to melting of one stemloop structure and the formation of an alternative structure that has Motif 1 displayed on its apical loop [19] . The position of MNV Motif 1 relative to the stop-start window is very similar to that of BM2 suggesting that the same remodelling could operate (Figures 4  and 8) . However, whilst transit and termination of the ribosome would destabilise the identified secondary structure (Figure 4) , liberating TURBS motif 1 in close proximity to helix 26, it is not clear whether this motif would subsequently be displayed as part of an alternative secondary structure. Whilst mfold analysis of the MNV region present locally upstream of the terminating ribosome does suggest an alternative secondary structure, further work will be needed to confirm this possibility.