How Does an IRES Work?
The IRES of the encephalomyocarditis virus (ECMV) permits the translation of two open reading frames from one messenger RNA. Although translation initiation of eukaryotic mRNAs occurs almost exclusively at the 5' cap, the IRES allows ribosomes to bind and initiate translation at a second, internal location. Thus, two proteins are expressed simultaneously from the same bicistronic mRNA transcript.