A nucleoside antibiotic. It inhibits protein synthesis by disrupting peptide transfer on ribosomes causing premature chain termination during translation. It is a potent translational inhibitor in both prokaryotic and eukaryotic cells. Resistance to puromycin is conferred by the puromycin N-acetyl-transferase gene (pac) from Streptomyces. Puromycin has a fast mode of action, causing rapid cell death at low antibiotic concentrations. Adherent mammalian cells are sensitive to concentrations of 2 to 5 µg/ml, while cells in suspension are sensitive to concentrations as low as 0.5 to 2 µg/ml.