Common laboratory strain used for recombinant protein expression.. Escherichia coli BL21(DE3)

Escherichia coli BL21(DE3). BL21(DE3) is a derivative of E. coli strain B. Deficiency in Lon and OmpT proteases makes it a superior host for recombinant protein expression. It also carries a DE3 recombinant phage harboring the T7 RNA polymerase gene that can direct high-level expression of cloned genes under the control of the T7 promoter.