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|Section2= |Section3= |Section4= |Section5= |Section6= |Section7= |Section8= }} 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).〔(【引用サイトリンク】title=G418 )〕 In general for bacteria and algae concentrations of 5 mg/L or less are used, for mammalian cells concentrations of approximately 400 mg/L are used for selection and 200 mg/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 mg/L up to 1400 mg/L. 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 ''Micromonospora rhodorangea'' produces many other gentamycins while producing G418. The common impurities of G418 include gentamycin X2, gentamicin A, gentamycin C1, C2, C1a and C2a.〔(G418 impurity profile )〕 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). Gentamycins have almost no selectivity, except gentamycin X2.〔(G418 selectivity )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「G418」の詳細全文を読む スポンサード リンク
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