A newly isolated antibiotic prevents aminoacyl-tRNA from entering the A site of a bacterial 30S ribosomal subunit but does not cause misreading. Which class is the new drug most likely to belong to?

• A. Macrolides, because they prevent tRNA binding by obstructing the peptide exit tunnel on the 50S subunit.
• B. Chloramphenicol, because it binds the 50S subunit and prevents tRNA from receiving peptide bonds by blocking aminoacyl-tRNA accommodation.
• C. Tetracyclines, because they bind 30S and sterically block tRNA binding to the A site.
• D. Aminoglycosides, because they bind the 30S subunit and cause strong inhibition of tRNA entry by inducing mRNA cleavage.

Answer: (C)