In eukaryotic translation, which initiation factor is responsible for scanning the 5' UTR from the 5' cap to locate the AUG start codon, and what feature of the mRNA context (Kozak sequence) determines start codon efficiency?
- A eIF2 (GTP-binding); AAAAUAAA near start codon
- B eIF4A (RNA helicase); GCC(A/G)CCAUGG consensus ✓
- C eIF6; internal ribosome entry site (IRES)
- D eIF3; 5' TOP (terminal oligopyrimidine tract)
Correct answer: B. eIF4A (RNA helicase); GCC(A/G)CCAUGG consensus
Explanation
The 43S preinitiation complex (containing the 40S subunit, eIF2-GTP-Met-tRNA, and accessory eIFs) is loaded onto the 5' cap by eIF4F (eIF4E, eIF4G, eIF4A). eIF4A, the RNA helicase, unwinds secondary structure in the 5' UTR during scanning. The Kozak consensus sequence GCC(A/G)CCAUGG (with the most critical positions being A/G at -3 and G at +4) determines the efficiency of start codon recognition by the 40S subunit. eIF2 provides the initiator Met-tRNA.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.