Internal Ribosome Entry Site
internal ribosome entry site
"Internal ribosome entry site (IRES) is a translational cis-acting element that directs ribosomes to the start codon by a cap-independent mechanism.  IRESs are usually about 450 nucleotides in length and were first identified in picornavirus RNAs.  IRESs can fold into a stable secondary hairpin structure to be incompatible with efficient translation by ribosomal scanning. (NCI)"