Effect of rare codons in C-terminal of green fluorescent protein on protein production in Escherichia coli.

In the previous study， the results on two interesting egfp genes indicated that the expressed eGFP production of egfp-codon containing multiple rare codons was 2.3-fold than that of egfp-genscript with mainly high-frequency-usage codons. Therefore， the rare codons also play important roles for the functional expression of genes and it is interesting to know which rare codons in the egfp affect the functional expression of eGFP. In this study， the structure-guided SCHEMA recombination method and site-specific mutagenesis were proposed to detect the contribution of the rare codons on the functional expression of eGFP. The 12 chimeric egfps were generated from egfp-codon and egfp-genscript by the software SCHEMA. The results indicated that it was the rare codons in the C-terminal coding region (residues from 147 to 239) of eGFP resulting in the higher expression levels in Escherichia coli. The single and multiple point mutations also indicated that the presence of rare codons in 3' coding regions of egfp could enhance the functional expression of eGFP in E. coli. Therefore， the gene sequence on the C-terminal could also affect its functional expression and the strategy of substituting rare codons into coding sequences might be an effective method for increasing heterologous proteins in the host.