Linezolid's mechanism of action is unique among protein synthesis inhibitors because it acts at:
- A 30S subunit, blocking A-site tRNA binding after initial codon recognition
- B 50S subunit, inhibiting peptidyl transferase and causing premature peptide release
- C 23S rRNA of the 50S subunit, preventing formation of the 70S initiation complex ✓
- D 30S subunit, causing misreading of mRNA codon-anticodon pairing
Correct answer: C. 23S rRNA of the 50S subunit, preventing formation of the 70S initiation complex
Explanation
Linezolid (an oxazolidinone) binds to domain V of the 23S rRNA component of the 50S subunit at a site that overlaps with the P-site, preventing the assembly of the 70S initiation complex (50S + 30S + mRNA + initiator fMet-tRNA). This step precedes elongation, so no peptide bond is ever formed. This unique site of action means there is no cross-resistance with other antibiotic classes. Option D describes aminoglycosides; option B describes chloramphenicol.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.