High-level misincorporation of lysine for arginine at AGA codons in a fusion protein expressed in Escherichia coli

Abstract

The expression of eukaryotic genes in Escherichia coli is one of the most frequently used tools of modern science. The arginine codon AGA is a common codon in eukaryotic genes but is particularly rare in E. coli. We report here 36 to 42% misincorporation of lysine at three AGA codons in a well-expressed protein. This misincorporation yields a protein whose electrospray mass spectrum (ESMS) shows peaks at the expected mass (M), M-28, M-56 and M-84 with intensities representing 34.5(+/-0.7), 37.5(+/-1.1), 21.2(+/-1.7) and 6.6(+/-0.5) % of the total intensity, respectively. Replacement of either all three AGA codons or the two closest to the 3' end of the gene by the more common CGC arginine codon gave a protein with a single ESMS peak. Misincorporation could also be eliminated by the co-expression of the tRNA(UCL)Arg gene, argU. These studies demonstrate that misincorporation of amino acids at rare codons of recombinant proteins can be far higher than previously thought.