Targeting the 18S rRNA:mRNA interaction using antisense oligonucleotides Termination-reinitiation on the BM2 ORF is likely to be dependent on interactions between the influenza B segment 7 RNA and helix 26 of the 18S rRNA [11] . However, other work has revealed that motif 1 may also be important in eIF3 binding [17] . To investigate the mRNA-18S rRNA interaction further, antisense 2-O-methyl oligonucleotides (AONs) were synthesised that would target either the loop of helix 26 of 18S rRNA ( Figure 2A ) or motif 1 of the BM2 TURBS ( Figure 2B ). Control oligonucleotides were also prepared to target sequences both upstream and downstream of motif 1 to control for potential nonspecific effects on translation ( Figure 2B ). An AON designed to target helix 26 of the 18S rRNA had no effect on BM2 synthesis ( Figure 2A ), although high concentrations (320-fold to 2960-fold molar excess of the AON to the mRNA) inhibited global translation ( Figure 2A and data not shown). Conversely, an AON targeting motif 1 specifically inhibited BM2 synthesis, with little effect on overall translation ( Figure 2B ). Importantly, the upstream and downstream control AONs had little effect on BM2 synthesis or global translation within the range tested for the BM2 motif 1 complementary AON ( Figure 2B ). It should be noted that the 80S ribosome will strip annealed AONs from the mRNA as it translates through the TURBS. However, both the upstream and motif 1 complementary AONs will be able to re-anneal once the ribosome reaches the UAAUG. However, it is possible that any effect of the downstream oligo is masked due to it being unable to reanneal in the presence of the terminating ribosome. Nevertheless, these data indicate that the effect of the BM2 motif 1 complementary AON is specific and not an effect on ribosome processivity, and provide further evidence in support of an interaction between motif 1 and 18S rRNA. However, we cannot rule out that these effects may also be due to perturbations of RNA secondary structure within the TURBS or due to interactions of motif 1 with an unspecified molecule (see later).