- Escherichia coli (E. coli) BL21(DE3) CodonPlus is a specialized derivative of the BL21(DE3) strain designed to improve the expression of eukaryotic genes that contain codons rarely used by E. coli.
- In heterologous expression, mismatched codon usage can significantly reduce protein yield, particularly for genes from humans, plants, or other organisms with GC-rich or complex codon bias.
- The CodonPlus strain addresses this limitation by supplying additional copies of tRNA genes for rare codons, such as AGG, AGA (Arg), AUA (Ile), CUA (Leu), CCC (Pro), and GGA (Gly). These tRNAs are carried on a plasmid, which is maintained using chloramphenicol selection.
- Like its parent strain BL21(DE3), CodonPlus contains the λDE3 lysogen encoding T7 RNA polymerase, allowing for strong, IPTG-inducible expression from T7 promoter-driven vectors. This makes the strain highly compatible with standard expression systems such as pET vectors. The enhanced tRNA supply not only improves translation efficiency but also reduces the risk of ribosomal stalling and premature termination of protein synthesis, leading to higher expression levels of full-length, functional proteins.
- This strain is especially beneficial when expressing eukaryotic proteins with unoptimized codon usage or when codon optimization is not feasible. However, the presence of the additional plasmid slightly increases the metabolic burden on the cell, and care must be taken to maintain both selection markers (typically ampicillin for the expression plasmid and chloramphenicol for the CodonPlus tRNA plasmid).
- Nonetheless, BL21(DE3) CodonPlus is a robust and effective choice for expressing difficult eukaryotic genes in a bacterial host.
