An extended RNA/RNA duplex structure within the coding region of mRNA does not block translational elongation

RNA/RNA duplex formation involving the 5'untranslated region of a mRNA can efficiently block translation. Here we investigated the effect on translation of an RNA/RNA duplex between part of the coding region and sequences of the 3'untranslated region of lysozyme mRNA. A cDNA was constructed which contained 2 identical sequences of 150 nucleotides, one of which was an inverted repeat of the other. Cell-free transcription of this cDNA with T7 RNA polymerase resulted in a mRNA with an extended RNA/RNA duplex within the coding region. The presence of the double stranded structure was confirmed by the accessibility of complementary oligonucleotides to this region. mRNA was cleaved by RNaseH, endogenous to the wheat germ lysate, when hybridization of a complementary oligonucleotide occurred outside but not within the predicted double stranded structure. When this mRNA was translated in a cell-free wheat germ translation system, the translation product was found to be of the size of full-length prelysozyme and not arrested. We conclude that the extend of a secondary structure within the coding region of a mRNA does not restrict the ability of the ribosome to translate this mRNA efficiently. Our data are consistent with the presence of an activity unwinding RNA/RNA duplexes, which is associated with the translating ribosome.