Leader Sequences of Eukaryotic mRNA Can Be Simultaneously Bound to Initiating 80S Ribosome and 40S Ribosomal Subunit

Binding of mRNA leader sequences to ribosomes was studied in conditions of a cell-free translation system based on wheat germ extract. Leader sequence of TMV mRNA (the so-called omega-RNA sequence) was able to bind simultaneously 80S ribosome and 40S ribosomal subunit. It was found that nucleotide substitutions in omega-RNA resulting in destabilization of RNA structure have no effect on the complex formation with both 80S ribosome and 40S ribosomal subunit. Leader sequence of globin mRNA is also able to form a similar joint complex. It is supposed that the ability of mRNA leader sequences to bind simultaneously 80S ribosome and 40S subunit is independent of leader nature and may reflect previously unknown eukaryotic mechanisms of translation initiation.