INITIATION OF PROTEIN-SYNTHESIS BY THE EUKARYOTIC TRANSLATIONAL APPARATUS ON CIRCULAR RNAS

The ribosome scanning model predicts that eukaryotic ribosomal 40S sub units enter all messenger RNAs at their 5' ends. Here, it is reported that eukaryotic ribosomes can initiate translation on circular RNAs, b ut only if the RNAs contain internal ribosome entry site elements, Lon g-repeating polypeptide chains were synthesized from RNA circles with continuous open reading frames. These results indicate that ribosomes can translate such RNA circles for multiple consecutive rounds and tha t the free 5' end of a messenger RNA is not necessarily the entry poin t for 40S subunits.