G418 (Geneticin) is an

aminoglycoside Aminoglycoside is a medicinal and bacteriologic category of traditional Gram-negative antibacterial medications that inhibit protein synthesis and contain as a portion of the molecule an amino-modified glycoside (sugar). The term can also refer ...

antibiotic similar in structure to

gentamicin B1 Gentamicin is an antibiotic used to treat several types of bacterial infections. This may include bone infections, endocarditis, pelvic inflammatory disease, meningitis, pneumonia, urinary tract infections, and sepsis among others. It is not ...

. It is produced by ''

Micromonospora rhodorangea ''Micromonospora'' is a genus of bacteria of the family Micromonosporaceae. They are gram-positive, spore-forming, generally aerobic, and form a branched mycelium; they occur as saprotrophic forms in soil and water. Various species are sources ...

''. G418 blocks

polypeptide synthesis Protein biosynthesis (or protein synthesis) is a core biological process, occurring inside cells, balancing the loss of cellular proteins (via degradation or export) through the production of new proteins. Proteins perform a number of critical ...

by inhibiting the elongation step in both

prokaryotic A prokaryote () is a single-celled organism that lacks a nucleus and other membrane-bound organelles. The word ''prokaryote'' comes from the Greek πρό (, 'before') and κάρυον (, 'nut' or 'kernel').Campbell, N. "Biology:Concepts & Connec ...

and

eukaryotic Eukaryotes () are organisms whose Cell (biology), cells have a cell nucleus, nucleus. All animals, plants, fungi, and many unicellular organisms, are Eukaryotes. They belong to the group of organisms Eukaryota or Eukarya, which is one of the ...

cells. Resistance to G418 is conferred by the neo gene from Tn5 encoding an aminoglycoside 3'-phosphotransferase, APT 3' II. G418 is an analog of

neomycin Neomycin is an aminoglycoside antibiotic that displays bactericidal activity against gram-negative aerobic bacilli and some anaerobic bacilli where resistance has not yet arisen. It is generally not effective against gram-positive bacilli and ...

sulfate, and has similar mechanism as

. G418 is commonly used in laboratory research to select genetically engineered cells . In general for bacteria and algae concentrations of 5 μg/mL or less are used, for mammalian cells concentrations of approximately 400 μg/mL are used for selection and 200 μg/mL 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/mL up to 1400 μg/mL. Resistant clones selection could require from 1 to up to 3 weeks.

G418 impurity profile

G418 is produced by fermentation and isolation processes and the G418 producing strain ''

'' produces many other gentamicins while producing G418. The common impurities of G418 include gentamicins A, C1, C1a, C2, C2a and X2. The quality of G418 is not based on just the potency, but more on the selectivity defined by the killing curve of the sensitive cells vs the resistant cells. A good G418 product has the lowest for sensitive cells (such as NIH 3T3) and the highest LD₅₀ (can be up to 5,000 μg/ml) for resistant cells (NIH 3T3 transfected with resistant genes). Gentamicins have almost no selectivity, except gentamicin X2.

Use in cell biology

G418 is routinely used as a selective agent in cell culture set-ups. Researchers can link the ''neoR'' selective resistance gene with their vector. Then if the vector is successfully introduced into cells, the cells can become G418-resistant cells. After treating with G418, these vector(-) cells will die, while vector(+) cells will survive. This method can help researchers select vector(+) cells.

References

{{reflist Aminoglycoside antibiotics Cell culture reagents Eukaryotic selection compounds