To determine whether the stimulation of frameshifting was specifically due to the bridging of the stem-loop with downstream sequence (the pseudo-pseudoknot), as opposed to the nonspecific presence of an RNA:DNA hybrid, the competing oligonucleotide (C-oligo) was designed to form a 15 bp duplex with JD366-18 mRNA, including the 3 0 Stem 2 forming region, which was expected to significantly out compete either the J-or R-oligos from binding to this site, thus disrupting formation of the pseudo-pseudoknot (see Figure 3A ). Additionally, in the presence of the C-oligo, the J-and R-oligos were still predicted to hybridize with the 5 0 Stem 2 forming region, enabling us to address the question of whether this interaction alone was able to stimulate frameshifting. The results demonstrate that the addition of the C-oligo severely inhibited the abilities of both the J-and R-oligos to promote efficient frameshifting ( Figure 6 ). These findings demonstrate that (i) frameshifting was specifically stimulated by bridging of the 5 0 and 3 0 Stem 2 forming regions by the J-and R-oligos, and (ii) that the presence of an RNA:DNA hybrid at the 5 0 Stem 2 forming region was not sufficient to stimulate frameshifting by itself.