Practice question

The 43S pre-initiation complex formed at the cap must unwind local secondary structure to reach the initiator AUG through linear scanning. This movement requires energy from ATP hydrolysis by DEAD-box RNA helicases, principally eIF4A as part of eIF4F, assisted by cofactors eIF4B, eIF4H, and helicases Ded1/DDX3 and DHX29 for more structured 5' UTRs containing stable stem-loops. ATP-driven conformational changes melt RNA duplexes, allowing progression of scanning complex. GTP hydrolysis powers eIF2 and eIF5B during initiator tRNA joining and subunit joining steps, but mechanical scanning itself depends predominantly on ATP helicase activity rather than GTPase cycles.