The dependence of BM2 synthesis on interactions between the mRNA and 18S rRNA raises the possibility that increasing 18S rRNA complementarity within motif 1 would lead to increased synthesis of the BM2fluc polypeptide. To test this, the bases adjacent to motif 1 were substituted such that the complementarity to 18S rRNA was increased to the 59, to the 39 or in both directions ( Figure 3A ). In all cases, however, the substitution mutations reduced the frequency of termination-reinitiation events, albeit to a lesser extent with the 39 complementary extension mutant ( Figure 3A ).