Principles of the GS Gene Expression System™
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Glutamine synthetase (GS) is the enzyme responsible for the biosynthesis of glutamine from glutamate and ammonium. This enzymatic reaction is the pathway for glutamine formation in a mammalian cell.
In the absence of glutamine in the growth medium, the GS enzyme plays an essential role in the survival of mammalian cells in culture. Some mammalian cell lines, such as mouse myeloma lines, do not express sufficient GS to survive without added glutamine. With these cell lines, a transfected GS gene can function as a selectable marker by permitting growth in a glutamine-free medium. Other cell lines, such as Chinese hamster ovary (CHO) cell lines, express sufficient GS to survive without exogenous glutamine. In these cases, the GS inhibitor, methionine sulphoximine, can be used to inhibit endogenous GS activity such that only transfectants with additional GS activity can survive.
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