As discussed above, the Gtx mRNA is thought to be able to recruit ribosomes by virtue of interactions between helix 26 of the 18S rRNA and the mRNA [28] [29] [30] ). It was therefore of interest to determine whether the minimal 7 nt Gtx motif could functionally replace motif 1. Two constructs were generated, one in which the inserted Gtx element was complementary to murine 18S rRNA (which would result in a mismatch with helix 26 of rabbit 18S rRNA) and one with full complementarity to the rabbit 18S rRNA, such that efficient tethering would be expected in rabbit reticulocyte lysates (RRL; Figure 3C , top-right panel). Termination-reinitiation was found to be inhibited in either mutant and to a similar extent as mutants in which a single nucleotide substitution was present to abolish 18S rRNA:mRNA base pairing ( Figure 3C ; the single nucleotide mutants have been described previously [11] ). These results suggest that motif 1 and the Gtx IRES element cannot functionally replace each other.