The E. coli BL21 strain is protease-deficient for optimal expression of a variety of recombinant proteins.

• High level expression of a variety of recombinant proteins
• Defective in E. coli strain B and wild-type restriction systems to permit high efficiency transformation with unmodified plasmid DNA
• Verified by RAPD fingerprint analysis using ready-to-go RAPD analysis kit
• Supplied lyophilised

Well suited for use with the GST gene fusion system, E. coli BL21 is an exemplary host for the expression of recombinant proteins. As an E. coli B strain, it further lacks the major protease, encoded by the lon gene, catalysing the endoproteolytic cleavage of damaged and recombinant proteins in the cell.

The protease-minus nature of BL21 makes it useful as an expression host. Since BL21 does not transform well, use an alternate strain for cloning and maintenance of the vector.

Genotype: The BL21 strain is derived from E. coli B. The genotype is F-, ompT, hsdS (rB -, mB -), gal, dcm.

Growth conditions: Resuspend lyophilised cultures in 1 ml of LB medium. Grow overnight at 37 °C before plating onto LB agar plates.

Storage conditions: −20 °C. Mix equal volumes of stationary phase culture (grown in LB medium) and glycerol. Store at –70 °C. Revive frozen glycerol stocks of BL21 by streaking onto LB agar plates.