Scanning of mRNA requires energy mainly in form of
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
Ref: Lodish Fig 4-22 eIF4A helicase ATP dependent; Alberts Chapter 6 - scanning requires ATP hydrolysis by eIF4A
