G-418 is used in the selection and maintenance of eucaryotic cells stably transfected with neomycin resistance genes. G-418 is an aminoglycoside antibiotic, related to Gentamicin, and exhibits toxicity towards both eukaryotic and prokaryotic cells. It is produced by Micromonospora rhodorangea and acts by binding the ribosome, thus inhibiting protein synthesis in both prokaryotic and eukaryotic cells.