production. The first IRES to be discovered was found in poliovirus RNA.

Poliovirus mRNA is translated as one long polypeptide. This polypeptide is then autocleaved by internal proteases into about 10 individual viral proteins. Not all cleavages occur with the same efficiency. Therefore, the amounts of proteins produced by the polypeptide cleavage vary: for example, smaller amounts of 3D^pol are produced than those of capsid proteins, VP1-4. These individual viral proteins are:thumb*3D^pol,