Cornell iGEM

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Wet Lab

E. coli DH5α

E. coli is a gram-negative, facultative anaerobic, rod-shaped bacterium that is the most widely studied prokaryotic model organism for work with recombinant DNA. We are using electrically competent and chemically competent DH5α strains that contain recA1 and endA1 mutations that increase insert stability and improve the quality of plasmid DNA prepared from minipreps.[1]

E. coli BL21

We are also using BL21 competent strains of E. coli, which are designed for high-efficiency protein expression of any gene under control of the T7 bacteriophage promoter system. T7 RNA Polymerase is regulated by arabinose induction and glucose inhibition of the araBAD promoter in its chromosomal DNA. Proteins under control of T7 promoter-driven vectors are then expressed at high levels. The cells also contain the T7 lysozyme gene within the pLysS plasmid, which suppresses T7 RNA polymerase activity caused by leaky basal expression.[2]


  1. Dh5-Alpha Competent E. coli. (2013). Retrieved from:
  2. Competent Cell BL21(DE3)pLysS. (2013). Retrieved from: