BL21-CodonPlus Competent Cells

Agilent BL21-CodonPlus competent cells dramatically improve protein expression in E. coli by overcoming codon bias. Codon bias occurs when forced high-level expression of a gene containing codons rarely expressed in E. coli depletes internal tRNA pools. This often results in poor protein synthesis, early termination of the polypeptide chain, or misincorporation of amino acids into the expressed protein. BL21-CodonPlus competent cells are derived from Agilent’s high performance BL21-Gold competent cell line. These cells enable efficient high-level expression of heterologous proteins in Escherichia coli.

Overcoming codon bias saves time and labor by eliminating the need for site-directed mutagenesis or for expressing the protein in a eukaryotic expression system. L21-CodonPlus competent cells are derivatives of BL21-Gold cells that have been engineered to include extra copies of genes that encode tRNAs for these rare E. coli codons. The additional availability of these tRNAs facilitates high level expression of many heterologous recombinant genes in BL21-CodonPlus competent cells. Efficient production of heterologous proteins in E. coli is frequently limited by the rarity of certain tRNAs that are abundant in the organisms from which the heterologous proteins are derived. Forced high-level expression of heterologous proteins can deplete the pool of rare tRNAs and stall translation.


BL21-CodonPlus competent cells also feature the Hte phenotype present in Agilent’s highest efficiency competent cell strain, XL10-Gold. The presence of the Hte phenotype increases the transformation efficiency of the cells. In addition, the gene that encodes endonuclease I (endA), an enzyme that rapidly degrades plasmid DNA isolated by most miniprep procedures, has been inactivated in these cells. These two features enable direct cloning of many protein expression constructs.