Practice question

Puromycin is aminonucleoside antibiotic mimicking 3' terminus of aminoacyl-tRNA with aromatic group linked via stable amide not labile ester. Puromycin enters ribosomal A-site accepting nascent polypeptide from P-site via peptidyl transferase, forming peptidyl-puromycin adduct that dissociates prematurely as truncated peptide bearing puromycin at C-terminus causing chain release independent of release factors. Resulting peptide targeted for degradation. At low concentrations used experimentally to label nascent chains and probe translation status, puromycin provides tool for polysome analysis. Resistance gene pac encoding N-acetyltransferase detoxifies antibiotic allowing selection of stable transformants expressing resistance widely used in mammalian cell engineering.