Mechanism
The mechanism of viral IRES function to date is better characterized than the mechanism of cellular IRES function, for which no clear mechanism have been proposed yet. Hepatitis C Virus-related IRESs directly bind 40S ribosomal subunit in such a way that their initiator codons are located in ribosomal P-site without mRNA scanning. These IRESs do not require Eukaryotic initiation factors eIF1, 1A, 4A, 4B, and 4E. Picornavirus IRES do not attract 40S directly, but rather through high-affinity eIF4G-binding site. In addition, many viral IRES (as well as cellular IRES) require additional proteins to mediate their function, known as IRES trans-acting factors (ITAFs). The role of ITAFs in IRES function is currently the subject of intense research.
Read more about this topic: Internal Ribosome Entry Site
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