( New BL21-Gold cells accelerate th...)High-efficiency Derivatives of the BL21 Series for Protein Expression

New BL21-Gold cells accelerate the protein expression process

Melody Jerpseth Bruce Jerpseth Lisa Breister Alan Greener
Stratagene

Stratagene has created variants of BL21 competent cells, the new BL21-Gold series. Epicurian Coli BL21-Gold * competent cells lack the EndA1 nuclease and offer 100-fold higher transformation efficiencies than the parental strains. These two features eliminate the process of first cloning and sequencing many protein expression constructs in an EndA strain and then retransforming the plasmids of interest into the BL21 strains for expression.

Epicurian Coli BL21 competent cells are the E. coli strains chosen for protein expression when a gene of interest is to be expressed from the T7 promoter.^## These strains have been engineered either to contain an inducible T7 RNA polymerase gene or to readily allow one to be introduced by phage infection.¹ BL21 competent cells contain a mutation in the ompT protease gene, which is implicated in the degradation of some recombinant proteins. BL21 cells are derivatives of E. coli B and naturally lack the Lon protease, which may affect the stability of some recombinant proteins.²

Although the BL21 cell series is engineered for protein expression, these strains have two significant problems that limit their use as primary transformation hosts. Because BL21 cells are derived from the E. coli B cell line rather than the E. coli K-12 cell line, their efficiency is relatively low (1 x 10⁶ cfu/g of pUC18 DNA). The other problem causing BL21 competent cell lines to be inadequate for initial transformation experiments is that they contain the EndA gene, which encodes an endonuclease that rapidly degrades miniprep DNA. This degradation makes restriction
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