BL21(DE3) electrocompetent E. coli cells are suitable for transformation, high-level protein expression and production of recombinant proteins in bacterial systems. The strain lacks the lon and ompT proteases thus promoting stability of recombinant proteins. BL21(DE3) strain carries a copy of the T7 RNA polymerase under control of the IPTG inducible lacUV5 promoter, and as a result, is ideal for controlled expression of both E. coli and T7 promoter driven constructs. BL21 (DE3)Êelectrocompetent cells are supplied as a pack of 10 single-use 50 _l/tube aliquots.The transformation efficiency is ³ 1x10⁸Êcfu/µg pBR322 plasmid DNA.