Putative implication of 3′-terminal segment of 18S rRNA in translation initiation of uncapped mRNAs in plants

Abstract

A putative implication 3′-terminal 18S rRNA segment in the cap-independent initiation of translation on plant ribosomes was studied. It was shown that 3′-terminal segment (nucleotides 1777–1811) of 18S rRNA including the last hairpin 45 was accessible for complementary interactions within 40S ribosomal subunits. Oligonucleotides complementary to this segment of rRNA, when added to wheat germ cell-free protein synthesizing system, specifically inhibited translation of uncapped reporter mRNA encoding β-glucuronidase. In the 5′-untranslated region (UTR), the reporter mRNA contained a leader sequence of potato virus Y (PVY) genomic RNA with fragments complementary to the region 1777–1811. A sequence corresponding to nucleotides 291–316 of PVY, which was complementary to most of the 3′-terminal 18S rRNA segment 1777–1808, was shown to enhance translational efficiency of the reporter mRNAs when placed into 5′-UTR. The obtained results suggest that complementary interactions between 5′-UTR of mRNA and 3′-terminal segment of 18S rRNA can take place during cap-independent translation initiation.