( High-level expression of difficul...)Codon Bias-Adjusted BL21 Derivatives for Protein Expression

High-level expression of difficult heterologous proteins

Carsten-Peter Carstens Anna Waesche
Stratagene

Stratagene has created variants of the Epicurian Coli BL21-Gold cells * called the BL21-CodonPlus -RIL series** of strains, which contain extra copies of the E. coli argU, ileY, and leuW tRNA genes. This modification allows for a high-level expression of proteins that are difficult to express in conventional E. coli hosts due to the codon bias of the gene of interest. The BL21-CodonPlus-RIL strains can eliminate the need to move the gene of interest into eukaryotic expression systems.

BL21-Gold(DE3) cells are the strain of choice for high-level production of heterologous proteins expressed from the T7-promoter. These strains have been engineered to contain an inducible T7-RNA polymerase. They are also EndA- to allow high-quality miniprep DNA preparation.¹ BL21 competent cells are derivatives of E. coliB and lack the Lon protease and the ompT protease genes that may cause instability and degradation of the recombinant protein.

Table 1
Rarest Codons (from E. coli) Preferred by Selected Organisms

Codon frequencies are expressed as codons used per 1000 codons encountered. A complete compilation of codon usage of the sequences placed in the gene bank database can be found at http://www.dna.affrc.go.jp/~nakamura/codon.html Codon frequencies of more than 15 codons/1000 codons are shown in bold to help identify a codon bias that may cause problems for high-level expression in E. coli. The arginine codons AGG and AGA are recognized by the same tRNA (pr
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