Several eukaryotic cell and viral mRNAs initiate translation by an alternative mechanism, which involves internal initiation rather than cap-dependent translation initiation. These mRNAs contain complex nucleotide sequences, called internal ribosomal entry sites (IRES) where ribosomes bind in a cap-independent manner and start translation at the closest downstream AUG codon. As an IRES element can direct binding of ribosomes to the start codons of multiple genes on a single message, it can support coexpression of more than one protein under the control of a single promoter.

 CAP-independent Translational Control DNA-based Vaccination RNA Capping Translational Control in Eukaryotes