Question

What Initiation factor is responsible for binding to IRES?

Answer 1

The initiation factor that binds to IRES is eukaryotic initiation factor-2 (eIF-2), which plays a critical role in the formation of the initiation complex necessary for the start of translation in eukaryotes.

Step-by-step explanation:

The initiation factor responsible for binding to Internal Ribosome Entry Sites (IRES) is known as eukaryotic initiation factor-2 (eIF-2). During the initiation phase of translation, eIF-2 binds to the small 40S ribosomal subunit in its GTP-bound form to start the process of protein synthesis. This is followed by the initiation complex scanning the 5'-UTR of mRNA until it locates the start codon AUG. Here, it enables the initiator tRNA to position itself correctly, after which the large 60S ribosomal subunit is recruited to form the completed initiation complex, allowing translation to proceed. This intricate process is tightly regulated by the phosphorylation status of eIF-2, which controls its ability to bind GTP and thus the formation of the initiation complex

Answer 2

The initiation factor responsible for binding to Internal Ribosome Entry Site (IRES) is eIF4G.

Step-by-step explanation:

Internal Ribosome Entry Site (IRES) is a sequence within the mRNA that allows for the initiation of translation in a cap-independent manner. In eukaryotic cells, translation initiation usually involves the eIF4F complex, comprising eIF4E, eIF4G, and eIF4A. However, in the presence of IRES, an alternative mechanism is employed. The initiation factor eIF4G directly binds to IRES, facilitating the recruitment of the ribosome to the mRNA.

This process allows for the initiation of translation without the need for a 5' cap structure, which is typical in cap-dependent translation initiation. Therefore, in IRES-mediated translation initiation, eIF4G plays a key role in binding to the IRES element.