The basic BL21 strain does not contain the T7 RNA polymerase gene and can be used with non-T7 RNA polymerase protein expression systems. This strain provides the tightest control of protein expression for extremely toxic proteins. BL21-Gold competent cells feature the high transformation efficiency phenotype (Hte) and have the gene encoding endonuclease I (endA) inactivated. Together, these two features allow direct cloning for most protein expression constructs. By cloning directly in the strain, you can save 2 days of work normally spent on subcloning procedures. The DE3 pLysS-derivatives of BL21 contain the pLysS plasmid codes for T7 lysozyme, a natural inhibitor of T7 RNA polymerase. This derivative provides tighter control for expression of toxic proteins.
For Research Use Only. Not for Use in Diagnostic Procedures.