Figure 3
From: A novel system for stable, high-level expression from the T7 promoter
Comparison of the expression levels of target proteins in  E. coli  with or without the selection of expressing cells. The SDS-PAGE results in B, C and D show the expression levels of the target protein from experiments B, C and D respectively. The numbers over each lane indicate how many hours passed between the induction with IPTG and the collection of the sample. ♦–experimental cultures: selection with kanamycin; ◊–control cultures: medium without kanamycin.