Low or non-existent protein synthesis, early termination, and misincorporation of amino acids in the expressed protein are common symptoms of codon bias, a common problem associated with conventional E.coli expression.
When you need to produce recombinant protein an E. coli expression system is always your first choice because it is fast, easy, and provides extremely high yields. However, sometimes E.coli expression fails due to the problem of codon bias. Our BL21-CodonPlus® competent cells* overcome expression problems caused by codon bias, providing high-level expression of many proteins that are difficult or impossible to express in conventional E. coli hosts.
Extra Codons Make the Difference
Expression of recombinant proteins in E. coli is difficult when the codon use in the recombinant gene differs from the codon use in the host cells. Forced high-level expression of a gene with codons that are rarely used by E. coli causes depletion of the of the internal tRNA pools. This leads to delayed translation of the recombinant RNA, resulting in degraded RNA or codon substitutions and misincorporations that destroy the functional characteristics of the protein. To solve this problem, we increased the supply of the rarest codons in E.coli to make expression of these proteins possible.
Choose the Right Strain for Your Genome
The problem of codon bias has been most thoroughly documented for the arginine codons AGA and AGG, which are the rarest codons in E. coli. However, codons for isoleucine (AUA), leucine (CUA), and proline (CCC) are also known to affect the amount and quality of protein produced in E. coli hosts (Table 1). Our BL21-CodonPlus® RIL strains contain extra copies of the E. coli argU, ileY, and leuW tRNA genes while the BL21-CodonPlus® RP strains contain the argU and proL tRNA genes. Use the -RIL strains for AT-rich genomes and the -RP strains for GC-rich genomes (Figures 1 and 2).
Expression Control Choices
BL21-CodonPlus derivatives offer different levels of expression control with T7 promoterdriven vectors, such as the Affinity® pCAL vectors**,*** and the pET vectors. The BL21-CodonPlus(DE3)-RIL and (DE3)-RP competent cells are all-purpose strains for high-level protein expression and easy induction with IPTG. When used with the CE6 bacteriophage, the BL21-CodonPlus-RIL and -RP cells provide the tightest control of protein expression, which is important for extremely toxic proteins. In addition, the BL21-CodonPlus-RIL and -RP cells are excellent hosts for non-T7 RNA polymerase expression systems.
*Patent pending.
See trademarks and licensing reference 3
** See trademarks and licensing reference 4
*** See trademarks and licensing reference 5
![(Table 1)](javascript:kl_openWin("images/p56Table1.gif",700,275);){kind=link}
![(Figures 1](javascript:kl_openWin("images/p57fig1.gif",825,425);){kind=link}