G-418 is a member of the large family of Aminoglycoside antibiotics and has a molecular structure almost like Gentamycin. The antibiotic is an irreversible inhibitor of protein synthesis. Due to its structure is capable of binding to both prokaryotic and eukaryotic ribosomes and inhibiting protein synthesis and generating errors in the transcription of the genetic code.
G-418 can by inactivated by NPTII or 3APH. The hydroxyl group present at the 3 position of G-418 is phosphorylated by NPTII. The resulting steriometric change of the molecular structure of the antibiotic prevents it from binding at its ribosome binding site.