( 10.9 ...)Codon Bias-Adjusted BL21 Derivatives for Protein Expression

10.9

18.4

6.0

9.8

12.6

5.2

Although strains of the BL21-Gold series are the most convenient and effective bacterial hosts for protein production presently available, expression of heterologous recombinant genes in E. coli is frequently limited when the codon usage in the recombinant gene differs from host cells (Table 1). Forced high-level expression of a gene, with codons that are rarely used by E. coli, results in depletion of the internal tRNA pools.² As a consequence, translation of the recombinant RNA species is delayed, leading to its enhanced degradation. The result of rare codon usage is most frequently seen as ineffective to nondetectable production of the target protein and the formation of aborted translation products that have the appearance of proteolytic degradation. In addition, rare codons may also affect the quality of the produced proteins by inducing translation frameshifts, codon skipping, and frequent misincorporation of amino acids. Misincorporation rates of up to 40% have been reported at specific rare arginine codons.³

The deleterious effects of rarely used codons have 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) have also been demonstrated to affect protein production and quality in E. coli hosts. The expression of affected recombinant genes can be salvaged either by synonymous replacement of the rare codons with more frequently used codons u
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