Aminoglycoside antibiotic related to gentamycin that inhibits prokaryotic and eukaryotic protein synthesis. Toxic to bacteria, yeast, protozoans, helminths, higher plant, and mammalian cells. Widely used in the selection of eukaryotic expression vectors carrying the bacterial neor/kanr genes. The product of these genes, aminoglycoside 3′-phosphotransferase, inactivates G418, neomycin, and kanamycin by phosphorylation. Introduction of either of these genes into cells can confer resistance to G418, which enables cells to grow in media containing G418.