Question

In E.coli, the chain initiating amino acid in protein synthesis is

• A. N-formyl methionine
• B. Methionine
• C. Glycine
• D. Serine

Answer 1

Answer: (A)

N-formyl methionine

N-formylmethionine is the chain initiating amino acid in protein synthesis in all prokaryotes while methionine is the chain initiating amino acid in protein synthesis in all eukaryotes. This means that formyl met tRNA is the first tRNA that binds to the P site in the complete 70S initiation complex in prokaryotes. AUG is the translation initiation codon but the same also codes for methionine. Thus, the initiation codon is read as fMet instead of methionine to differentiate as the first codon. Methionine and N-formyl methionine are encoded by single codon. Methionine confers advantage to be used as initiation amino acid.

Thus, the correct answer is option A.