G418

G418 (Geneticin) is an aminoglycoside antibiotic similar in structure to gentamicin B1. It is 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 neo gene from Tn5 encoding an aminoglycoside 3'-phosphotransferase, APT 3' II. G418 is commonly used in laboratory research to select genetically engineered cells (typically using the KanMX selectable marker). In general for bacteria and algae concentrations of 5 μg/L or less are used, for mammalian cells concentrations of approximately 400 μg/L are used for selection and 200 μg/L for maintenance. However, optimal concentration for resistant clones selection in mammalian cells depends on the cell line used as well as on the plasmid carrying the resistance gene, therefore antibiotic titration should be done to find the best condition for every experimental system. Titration should be done using antibiotic concentrations ranging from 100 μg/L up to 1400 μg/L. Resistant clones selection could require from 1 to up to 3 weeks.