• Selection of transfected cells in presence of antibiotics such as neomycin, hygromycin and puromycin.
– Expression of r-proteins can increase by exposing cells to methotrexate (MTX)
– MTX can block the activity of DHFR
– After 2-3 weeks of the MTX exposure only cells which overproduce DHFR can survive
Glutamine Synthetase (GS) gene expression system
- Expression vector encoading product gene plus GS gene, allowing glutamine synthesis
- GS is inhibited by methionine sulphoximine (MSX)
- Selection in the glutamine free medium for GS minus cell types(e.g.NSO)
- Selection in the presence of MSX for GS positive cell types (e.g. CHO)
- Only cells with GS gene - selects for rare integration into transcriptionally efficient cites in genome
- Expression of linked product gene, driven by strong promotor, enhanced by favourable integration sites.
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