In RHDV and FCV, TURBS motifs 1 and 2 are separated by some 30 nt, much of which appears to be non-essential [15] [16] [17] 19] . However, given that the minimal sequence requirement for termination-reinitiation of BM2 (,45 nt; [11] ) is shorter than that documented in the caliciviruses (69 and 87 nt; [15, 17, 19] ), we wished to test whether any of the residues were non-essential. To do this, we introduced 6 nt deletions throughout the length of the sequence upstream of the M1 termination codon in the context of the BM2 termination-reinitiation reporter plasmid, p2luc-BM2-204 ( Figure 1A ; [11] ). As expected, translation of the BM2-204 reporter mRNA generated products corresponding to the capdependent upstream product (rlucM1-204 ,36 kDa) and the termination-reinitiation product (BM2fluc ,62 kDa). The latter protein was not observed in translations of the negative control reporter mRNA, p2luc-BM2ps (rluc'M1 ,33 kDa, [11] ), which contains an in-frame stop codon immediately upstream of the TURBS. Significantly, deletion of any part of the minimal required region led to a strong inhibition of BM2fluc synthesis, suggesting that the entire TURBS is required for efficient termination-reinitiation on the segment 7 RNA ( Figure 1A ). Alternatively, it was possible that the defect in BM2 synthesis in this deletion series may be a consequence of the altered spacing between the M1 stop codon and upstream features required for termination-reinitiation. To test this, we selected three of the 6 nt deletion mutants surrounding motif 1 (mutants 6.1, 6.4 and 6.6) and replaced the deleted regions with two different random 6 nt sequences ( Figure 1B ). No restoration of BM2 synthesis was observed with either of the 6.1 nucleotide replacement mutants ( Figure 1B) . Replacement of nucleotides into the 6.4 deletion mutant had no effect with the first of the mutants (6.4r1), but some recovery was observed in the second of these mutants (6.4r2), albeit the frequency of termination-reinitiation was diminished compared to that of the wild-type mRNA ( Figure 1B ). In contrast, insertion of 6 nt back into the 6.6 deletion mutant fully restored BM2 synthesis in both cases ( Figure 1B) . These results suggest that the minimal 45 nt TURBS region is split into both sequencespecific and sequence-independent elements, where the sequence towards the 59 end of the minimal region is important in basespecific interactions, whereas the 39 end of the TURBS may act solely as a spacer, important in placing motif 1 relative to the terminating ribosome.