As opposed to mfold 1, the structure presented for mfold 2 would still be able to form when the ribosome has translated through the upstream ORF and is in the process of termination. We tested this structure in the same way, by introducing destabilising mutations independently in both arms at the base of stem 29 (creating mutants p2luc-BM2A1' and p2luc-BM2A29) and preparing a double mutant that would yield a pseudowild-type structure, which would be expected to exhibit BM2fluc synthesis (p2luc-BM2A19/29). It should be noted that the A19 mutation is very similar to that of the A1-2/ 3 nt mutant, given that this arm base pairs to form both stem 2 and stem 29 in the two putative folds. As expected, this mutation dramatically inhibited synthesis of BM2fluc similarly to that observed with the A1 mutation ( Figure 8B ). However, as before, no inhibition of BM2 synthesis was observed when stem 2 was destabilised in the 39 arm ( Figure 8B ). Nevertheless, the partial restoration of BM2 expression (to around 50% of wild-type) seen with the A19/29 double mutant, indicates that base-pairing in this region may play some role in termination-reinitiation. The simplest conclusion from these experiments, however, is that neither mfold 1 nor mfold 2 represent the sole active confirmation, although it is possible that these mutants may form another structure that can present the TURBS motif 1 to helix 26 of 18S rRNA.