Translation initiation in prokaryotes: Which modified amino acid is used at the start of most prokaryotic proteins during translation initiation?

Introduction / Context:
Protein synthesis in bacteria begins uniquely with a specialized initiator tRNA charged with a modified amino acid. Recognizing this initiator residue is essential for understanding translation initiation, ribosome assembly, and how bacterial proteins are distinguished from eukaryotic ones.

Given Data / Assumptions:

• Bacterial initiation uses a dedicated tRNA (tRNA^fMet).
• The first amino acid in most bacterial proteins is chemically modified before incorporation.
• Question asks for the specific modified residue’s name.

Concept / Approach:

In bacteria, methionine is formylated to N-formylmethionine (fMet) and delivered to the P-site by initiation factors along with the small ribosomal subunit at the start codon (usually AUG, occasionally GUG or UUG reinterpreted as start).

Step-by-Step Solution:

Verification / Alternative check:

Proteomic studies show N-terminal formyl groups are often deformylated post-translationally, but initiation still uses fMet. Eukaryotes instead start with methionine (not formylated), supporting the distinction.

Why Other Options Are Wrong:

N-formylserine/leucine/alanine are not the bacterial initiator residues.

Common Pitfalls:

Confusing bacterial fMet initiation with eukaryotic Met initiation or with mitochondrial translation, which resembles bacterial mechanisms but is context specific.

Final Answer:

N-formylmethionine