During translation of a eukaryotic mRNA, the 43S pre-initiation complex scans from the 5' cap toward the start codon. When the anticodon of Met-tRNAi recognises the AUG start codon, a GTP hydrolysis event catalysed by which factor triggers release of eIFs and allows 60S subunit joining?

• A eIF4A unwinds secondary structure and hydrolyses GTP at AUG
• B eIF5 stimulates GTP hydrolysis by eIF2, releasing eIF2·GDP and other factors ✓
• C eIF3 directly hydrolyses GTP to release the 40S subunit
• D eIF6 hydrolyses GTP to allow 60S subunit anti-association factor removal

Explanation

When the initiator Met-tRNAi·eIF2·GTP ternary complex base-pairs with the AUG codon, eIF5 (a GTPase-activating protein) stimulates intrinsic GTPase activity of eIF2, converting eIF2·GTP to eIF2·GDP. This conformational change causes the eIF complex to dissociate, allowing eIF5B (with its own GTP) to facilitate 60S subunit joining, forming the 80S initiation complex. eIF2B (a guanine nucleotide exchange factor) subsequently recharges eIF2 with GTP. Phosphorylation of eIF2α (by HRI, PKR, GCN2, PERK) sequesters eIF2B and globally represses translation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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