Which feature contributes to efficient translation initiation in eukaryotes around AUG?

• A. A GC-rich promoter upstream
• B. A purine at -3 and a G at +4 relative to AUG
• C. A poly-A tail upstream
• D. A TATA box immediately before AUG

Answer: (B)

The essential idea is the Kozak sequence context around the start codon, which guides the eukaryotic ribosome to initiate translation at AUG. A purine at position -3 and a G at position +4 relative to AUG create the strongest context for recognition by the initiation machinery, helping the initiator tRNA and initiation factors align AUG correctly during scanning. This surrounding sequence around AUG directly boosts how efficiently translation starts.

The other options involve elements that control transcription or mRNA processing rather than initiation of translation. A GC-rich promoter upstream and a TATA box are promoter features that affect transcription initiation, not the ribosome’s recognition of AUG. A poly-A tail upstream doesn’t reflect a real feature of mRNA and is not involved in start-site recognition.