G418 G418 is an aminoglycoside antibiotic similar in structure to gentamicin B1, produced by Micromonospora rhodorangea. G418 blocks polypeptide synthesis by inhibiting the elongation step in both prokaryotic and eukaryotic cells. Resistance to G418 is conferred by the Neomycin resistance gene (neo) from Tn5 encoding an aminoglycoside 3‘-phosphotransferase, APH 3‘ II. Selection in mammalian cells is usually achieved in three to seven days with concentrations ranging from 400 to 1000 µg/ml. Cells that are dividing are affected sooner than those that are not. Working concentration: 400 to 1000 µg/ml in mammalian cells CAS number: 108321-42-2 Molecular weight: 692.7 Formula: C20H40N4O10. 2H2SO4