Start signal: The AUG codon, which codes for methionine, plays what specific role at the beginning of translation?

Introduction / Context:
Translation begins at a defined start codon that sets the reading frame. In nearly all organisms, AUG serves this role, coding for methionine (Met) or N-formyl methionine (fMet) in bacteria.

Given Data / Assumptions:

• AUG specifies methionine.
• At initiation, special initiator tRNAs recognize AUG at the ribosomal P site.
• Question asks for AUG’s functional role at the start.

Concept / Approach:
AUG functions as the initiation codon, defining the reading frame and recruiting initiation factors and the initiator tRNA. Subsequent AUGs within the frame are read by elongator tRNAs during elongation.

Step-by-Step Solution:

Verification / Alternative check:
Kozak (eukaryotes) and Shine–Dalgarno (prokaryotes) sequences help position AUG for initiation, reinforcing its role.

Why Other Options Are Wrong:

• Elongation codon: elongation uses many sense codons, but “initiation” is specific.
• Termination: stop codons are UAA/UAG/UGA.
• Propagation: non-standard term.

Common Pitfalls:
Assuming every AUG is a start codon; context and signals determine whether an AUG initiates translation.

Final Answer:
Initiation codon (start signal)