质粒稳定性测试
Immediately before indcution, it is advisable to test the culture to determine the fraction of cells that still carry the target plasmid. This involves plating of cells on苹果7怎么截图 four different plates.
Plate | cells that grow on the plate |
LB plate | all viable cells |
LB plate + antibiotic | 载沣简介cells that still carry the plasmid |
LB plate + IPTG (1 mM) | cells that have lost the plasmid or mutants that have lost the ability to express the target gene |
忆往昔LB plate + antibiotic + IPTG (1 mM) | 评剧花为媒报花名only mutants that retain the plasmid but have lost the ability to express the target gene |
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Remarks
In the prence of IPTG, cells carrying a protein production plasmid do not grow becau have dedicated all their resources to the production of the recombinant protein instead of cell maintainance.
口味重In the prence of the pLysS vector, IPTG also prevents colony formation except with certain vector (such as pET-3 and some vectors carrying the T7lac promoter). In the prence of pLysE , IPTG usually does not prevent colony formation unless the target protein is toxic.
In a typical culture uful for producing target protein, almost all cells will form colonies both on the LB plate and on the LB plate + antibiotic; less than 2% of the cells will form a colony on the LB plate + IPTG; and less than 0.01% will form a colony on the LB plate + antibiotic + IPTG.章鱼丸
With unstable target plasmids, the fraction of cells that have lost the plasmid will be reflected by an increa in colonies on the LB plate + IPTG and a decrea on ther LB plate + antibiotic.
Protocol
1. Immediately before induction with IPTG (at OD600 is approx. 0.6), take a 100-m 大蒜烧肉l aliquot of the cell culture.
2.Make a rial dilution of the cell suspension, including a 105 and 106 dilution.
3. Plate cells at a dilution of 105 on the LB plate + IPTG and on the LB plate+ IPTG + antibiotic .Plate cells at a dilution of 106 on the LB plate and on the LB plate +antibiotic .
4. Incubate the plates overnight a 37°C.
5. Count the number of colonies on each plate.
Reference: pET System Manual, 8th ed., 1999 (Novagen).
